What Are the Core Issues Litigated in a Japanese Patent Infringement Lawsuit?

Navigating a patent infringement lawsuit in Japan requires a thorough understanding of several core legal and factual questions that form the battleground between patentees and alleged infringers. These lawsuits are not monolithic; they involve a structured examination of distinct issues, each carrying its own set of rules, precedents, and strategic considerations. While the ultimate question is whether infringement has occurred and what remedies are appropriate, the path to that answer is paved with detailed arguments on several key fronts.

Broadly, a Japanese patent infringement action compels the court to dissect the dispute into four primary areas of inquiry:

1. The Technical Scope of the Patented Invention: Does the accused product or process fall within the protected boundaries of the patent claims?
2. The Act of "Working" the Invention: Has the defendant engaged in an act that legally constitutes "working" (実施 - jisshi) the patented invention?
3. Applicability of Defenses Limiting Patent Rights: Even if the act falls within the technical scope and constitutes "working," are there legal or equitable doctrines that limit or negate the patentee's right to enforce the patent against the defendant?
4. Patent Invalidity: Is the patent itself valid, or does it suffer from a fatal flaw that renders it unenforceable?

Understanding how these core issues are framed and litigated is crucial for any party involved in, or seeking to avoid, patent disputes in Japan.

I. The Pivotal Question: Does the Accused Product/Process Fall Within the Technical Scope of the Patented Invention?

This is often the most contentious and technically complex part of an infringement suit. The determination of whether an accused product or process (often referred to as the "accused instrumentality" or 被疑侵害物件 - higi shingai bukken) infringes a patent begins with defining the scope of the patentee's rights.

A. Claim Construction: The Starting Point

The foundation of this inquiry lies in claim construction (クレーム解釈 - kurēmu kaishaku). The claims of a patent define the invention for which protection is granted. Article 70(1) of the Japanese Patent Act stipulates that the technical scope of a patented invention shall be determined based on the statements in the patent claims attached to the application.

However, Article 70(2) clarifies that in determining this technical scope, the meaning of the terms used in the claims shall be interpreted by also considering the description (明細書 - meisaisho) and drawings (図面 - zumen) attached to the application. This means that while the claims are paramount, they are not read in a vacuum. The specification provides the context and lexicography for the claim language. Historically, there was some debate about whether the approach to claim construction differed between infringement litigation (where Article 70(2) explicitly allows broader reference to the specification) and invalidity proceedings (where a stricter, more literal approach to claims was sometimes advocated, as seen in the Supreme Court decision of March 8, 1991, Minshu Vol. 45, No. 3, p. 123, often referred to as the "Lipase" case ). However, the prevailing trend in recent court practice, especially after the introduction of the invalidity defense in infringement litigation (discussed later), is towards a unified approach to claim interpretation across both contexts to avoid procedural inefficiency and inconsistent outcomes.

The process of claim construction involves meticulously analyzing the language of each claim element, often breaking down complex claims into their constituent parts. The objective is to ascertain the precise boundaries of the invention as understood by a person skilled in the art (当業者 - tōgyōsha) at the time of filing.

B. Literal Infringement: Meeting All Claim Elements

The first test for infringement is literal infringement (文言侵害 - mongon shingai). This occurs if the accused instrumentality incorporates each and every element recited in a patent claim. This is often referred to as the "all-elements rule." If even one element of a claim is not found in the accused product or process, there is generally no literal infringement of that claim.

Disputes frequently arise over the precise meaning and scope of the terms used in the claims. Parties will present arguments, often supported by expert testimony and technical evidence, on how a person skilled in the art would understand the claim language in light of the specification, drawings, and the state of the art at the relevant time.

C. Beyond Literal Wording: The Doctrine of Equivalents

If literal infringement is not found, the inquiry does not necessarily end. Japanese patent law, like that of many other jurisdictions, recognizes the Doctrine of Equivalents (均等論 - kintōron). This doctrine allows a court to find infringement even if the accused product or process does not fall within the literal scope of the patent claims, provided certain conditions are met.

The seminal Supreme Court decision of February 24, 1998 (Minshu Vol. 52, No. 1, p. 113, the "Ball Spline Bearing" case) established a five-part test for the application of the doctrine of equivalents. Broadly, these conditions involve assessing whether the differing element in the accused product is an insubstantial change, performs substantially the same function in substantially the same way to achieve the same result, and whether its interchangeability was foreseeable by a person skilled in the art at the time of infringement. The doctrine also considers whether the accused equivalent was obvious over the prior art at the time of filing and whether it was intentionally excluded from the claims during prosecution (prosecution history estoppel or 包袋禁反言 - hōtai kinhangen). The application of this doctrine is complex and highly fact-specific.

D. Indirect Infringement: Addressing Contributory Acts

In some cases, an accused product may not itself be the complete patented invention but rather a component or material part thereof, supplied or offered for supply by the defendant. If this component is specifically adapted for use in the patented invention and has no substantial non-infringing uses, its provision may constitute indirect infringement (間接侵害 - kansetsu shingai) under Article 101 of the Patent Act.

Japanese law distinguishes between different types of indirect infringement, such as providing an item that is "only used" for the working of the patented invention (a dedicated component) or providing an item that, while potentially having other uses, is an "indispensable" or "essential element" for solving the problem addressed by the patented invention, coupled with the supplier's knowledge (or constructive knowledge) of its use in an infringing manner. This area of law is also intricate, with specific requirements for establishing each type of indirect infringement.

II. The Accused Act: Does it Constitute "Working" of the Patented Invention?

Even if an accused product or process falls within the technical scope of a patent, infringement only occurs if the defendant has engaged in an act defined as "working" (実施 - jisshi) the invention in the course of trade.

A. Statutory Definition of "Working" (Jisshi)

Article 2(3) of the Patent Act defines "working" differently depending on the category of the invention:

• For an invention of a product (物の発明 - mono no hatsumei): Acts of producing, using, assigning (譲渡 - jōto), leasing (貸渡し - kashiwatashi), importing, or offering for assignment or lease (including displaying for the purpose of assignment or lease) the product. For inventions of software programs, "working" also includes providing the program via a telecommunications line.
• For an invention of a process (方法の発明 - hōhō no hatsumei): Acts of using the process.
• For an invention of a process for manufacturing a product (物を生産する方法の発明 - mono o seisan suru hōhō no hatsumei): In addition to using the process, acts of using, assigning, leasing, importing, or offering for assignment or lease the product manufactured by that process.

The term "production" (生産 - seisan) in the context of product inventions is interpreted broadly and can include not only manufacturing from raw materials but also assembling components into a finished product, or even repairing or modifying an existing product to such an extent that it is considered a new production of the patented item.

B. The "In the Course of Trade" (業として - gyō to shite) Requirement

Article 68 of the Patent Act states that a patentee has the exclusive right to work the patented invention "in the course of trade" (or "as a business"). This generally excludes purely private, non-commercial acts from the scope of infringement. However, "in the course of trade" is not limited to profit-making activities; it can encompass a wide range of commercial and industrial activities, even if not directly for profit, as long as they are not purely personal or household use.

III. Defenses: Limitations on Patent Rights

If the court finds that the accused instrumentality falls within the patent's technical scope and the defendant's act constitutes "working," the defendant may still avoid liability by successfully asserting certain defenses that limit the patentee's rights.

A. Exhaustion of Rights (Shōjin)

A fundamental principle in Japanese patent law (though not explicitly codified in a single statutory provision for all situations, it is a well-established judicial doctrine) is the exhaustion of patent rights (消尽 - shōjin or 権利消尽 - kenri shōjin). Once a patented product has been legitimately sold or otherwise put into the stream of commerce in Japan by the patentee or with their consent, the patentee's rights with respect to that particular item are generally considered exhausted. This means that subsequent purchasers are typically free to use, resell, or repair that item without infringing the patent.

The doctrine has complexities, particularly concerning repair versus reconstruction of a patented product, and its application to products first sold outside Japan (international exhaustion), which was notably addressed by the Supreme Court on July 1, 1997, in the "BBS Wheels" case (Minshu Vol. 51, No. 6, p. 2299).

B. Prior User Rights (Senshiyō-ken)

Article 79 of the Patent Act provides a defense for a party who, without knowledge of the content of an invention claimed in a patent application, had independently made the invention or learned it from someone who independently made it, and was working or preparing to work the invention in Japan at the time the patent application was filed (or its priority date). Such a prior user is generally entitled to a non-exclusive license to continue working the invention within the scope of their existing business or preparations. Establishing this right involves proving the independent creation or acquisition of the invention and the extent of the business or preparations prior to the critical date.

C. Experimental or Research Use (Shiken matawa Kenkyū)

Article 69(1) of the Patent Act states that the effects of a patent right shall not extend to the working of the patented invention for the purposes of experiment or research. This exemption is crucial for technological advancement, allowing others to study and test a patented invention.

However, the scope of this exemption is not unlimited. It generally does not cover activities that are primarily commercial in nature, even if they have some experimental aspect. A significant area of interpretation involves clinical trials conducted for obtaining regulatory approval for generic drugs. The Supreme Court decision of April 16, 1999 (Minshu Vol. 53, No. 4, p. 627) clarified that such activities can fall within the experimental use exemption, provided they are strictly for the purpose of obtaining said approval and do not extend to stockpiling for post-expiry sales.

D. Other Limiting Doctrines/Provisions

Other defenses or limiting principles might arise depending on the facts:

• Publicly Known Technology (Kōchi Gijutsu no Kōben): Historically, courts sometimes recognized a defense based on the accused infringing act merely practicing technology that was already publicly known before the patent's filing. However, this defense is now largely subsumed within the broader invalidity defense, where the novelty or inventive step of the patent is challenged.
• Prosecution History Estoppel (Hōtai Kinsokugen or Izon-teki Jōkō): Statements or amendments made by the applicant during patent prosecution to overcome rejections or distinguish the invention from prior art can prevent the patentee from later re-capturing that surrendered subject matter through a broad claim interpretation or the doctrine of equivalents.
• Hypothetical Claim (Kasōteki Kurēmu): In the context of the doctrine of equivalents, a court will consider whether a hypothetical claim broad enough to literally cover the accused equivalent would have been patentable over the prior art at the time of filing. If not, the doctrine of equivalents cannot be used to extend protection to such an equivalent.

IV. Challenging the Patent Itself: The Invalidity Defense

A powerful and frequently used defense in Japanese patent infringement litigation is to attack the validity of the patent itself. Article 104-3 of the Patent Act explicitly allows a defendant in an infringement suit to assert that the patent should be invalidated (無効の抗弁 - mukō no kōben). If the court finds that grounds for invalidity exist, the patent right cannot be enforced against the defendant in that litigation, even if a separate invalidation trial before the Japan Patent Office (JPO) has not been concluded or even initiated.

A. The Invalidity Defense in Infringement Litigation

This defense effectively allows the infringement court to make a de facto determination of patent validity for the purpose of the infringement suit. It was formally codified following the Supreme Court's landmark decision in the "Kilby" case (April 11, 2000, Minshu Vol. 54, No. 4, p. 1368), which held that asserting a patent right that is "clearly" invalid constitutes an abuse of rights. The "clear" invalidity threshold is no longer a strict requirement under Article 104-3, and courts now conduct a full examination of the alleged invalidity grounds if properly raised.

B. Key Grounds for Patent Invalidity

The grounds for invalidity largely mirror the requirements for patentability:

• Lack of Patentable Subject Matter (Art. 2(1)): The claimed subject matter does not meet the statutory definition of an "invention" (e.g., it's a mere discovery, a law of nature, an abstract idea, or a business method per se without technical character).
• Lack of Industrial Applicability (Art. 29(1), main part): The invention cannot be used in industry (e.g., certain medical treatment methods performed on the human body).
• Lack of Novelty (新規性 - shinki-sei) (Art. 29(1)): The invention was publicly known, publicly worked, or described in a distributed publication or made available to the public through telecommunication lines anywhere in the world before the filing or priority date.
• Lack of Inventive Step (進歩性 - shinpo-sei or 非容易推考性 - hi-yōi suikō-sei) (Art. 29(2)): The invention would have been easily conceivable by a person skilled in the relevant art based on the prior art existing before the filing or priority date.
• First-to-File Principle and Related Issues (Art. 39, Art. 29-2): Conflicts with prior patent applications. For example, double patenting or an invention described in an earlier-filed but later-published application.
• Defective Specification (記載要件不備 - kisai yōken fubi):
  • Enablement Requirement (実施可能要件 - jisshi kanō yōken) (Art. 36(4)(i)): The description in the specification is not clear and sufficient enough to enable a person skilled in the art to work the invention.
  • Support Requirement (サポート要件 - sapōto yōken) (Art. 36(6)(i)): The invention described in the claims is not supported by the description in the specification (i.e., the claims are broader than what the specification justifies).
  • Clarity Requirement (明確性要件 - meikakusei yōken) (Art. 36(6)(ii)): The claims are not clear.

If the defendant successfully proves any of these grounds, the patent may be treated as unenforceable in the context of that specific lawsuit.

V. A Note on Factual Allegations and Burden of Proof (Yōken Jijitsu)

Japanese civil procedure, including patent litigation, places significant emphasis on the structured pleading of material facts (要件事実 - yōken jijitsu) that correspond to the legal requirements for a claim or defense. The allocation of the burden of proof generally follows the "modified legal requirement classification theory" (修正法律要件分類説 - shūsei hōritsu yōken bunrui setsu), a framework used by Japanese courts to assign which party must plead and prove specific facts.

In essence:

• The plaintiff (patentee) bears the burden of proving the elements of their infringement claim: ownership of a valid patent, the defendant's accused act, and that this act falls within the technical scope of the patented invention. For damages, the plaintiff must also prove the fact of damage and its amount (though presumptions under Article 102 can assist here).
• The defendant bears the burden of proving affirmative defenses, such as exhaustion, prior user rights, or the facts supporting an invalidity claim (e.g., the existence of prior art that destroys novelty or inventive step).

The diagrammatic representation of claims, defenses, and counter-defenses (請求原因 - seikyū gen'in, 抗弁 - kōben, 再抗弁 - sai-kōben) helps visualize the logical structure of arguments and the allocation of proof burdens in a patent infringement suit.

VI. Conclusion

Patent infringement lawsuits in Japan are complex proceedings involving a rigorous examination of multiple, often intertwined, legal and technical issues. The determination of whether an accused product or process falls within the technical scope of a patent, whether the defendant's actions constitute "working" the invention, the applicability of various defenses, and the underlying validity of the patent itself are all critical facets of the litigation. Successfully navigating these core issues demands not only a deep understanding of Japanese patent law and procedure but also meticulous factual investigation, robust technical analysis, and astute legal strategy.