My Competitor is Infringing My Japanese Patent! What Constitutes Literal Infringement?

Japanese Attorney at Law - Bengoshi L.L.

• 8 min read

Discovering that a competitor's product or process appears to be using your patented technology can be a significant concern for any patent holder. In Japan, the most direct way to establish patent infringement is through literal infringement (文言侵害 - mongon shingai). This involves demonstrating that the accused product or process falls squarely within the precise wording of your patent claims. Understanding the principles of literal infringement is crucial for both enforcing your patent rights and for assessing potential infringement risks from competitors.

This article delves into what constitutes literal infringement under Japanese patent law, focusing on the "all elements rule" and how patent claims are meticulously compared to an accused product or process.

I. The Foundation: Technical Scope Defined by Patent Claims (Article 70, Patent Act)

Before analyzing infringement, one must first understand what the patent protects. The legal boundary of a patented invention is known as its "technical scope" (技術的範囲 - gijutsu-teki han'i).

A. Claims are Paramount in Defining Technical Scope

Article 70(1) of the Japanese Patent Act unequivocally states: "The technical scope of a patented invention must be determined based on the statements in the patent claims attached to the request."
This means the patent claims (特許請求の範囲 - tokkyo seikyū no hani) are the definitive starting point and the ultimate measure of what is protected. What is not claimed is not protected, regardless of what might be disclosed in other parts of the patent document.

B. Interpreting the Language of the Claims

While the claims themselves are primary, their language is not read in a vacuum. Article 70(2) clarifies: "In the case referred to in the preceding paragraph, the meaning of terms used in the patent claims shall be interpreted by also considering the statements in the specification (excluding the patent claims) and the drawings attached to the request."

  • The specification (明細書 - meisaisho), particularly the "Detailed Explanation of the Invention" section, serves as an intrinsic dictionary, providing context and potentially defining terms used in the claims.
  • Drawings (図面 - zumen) illustrate the invention and aid in understanding the claimed elements and their relationships.
  • The perspective of a Person Skilled in the Art (PSA) at the time of filing is generally used to understand how claim terms would have been interpreted in the relevant technical field.

However, it's a crucial principle that the specification and drawings are used to clarify the meaning of the existing claim terms, not to import limitations from the specification into the claims if those limitations are not already part of the claim language itself.

It's also important to note that the abstract (要約書 - yōyakusho) of the patent cannot be used for interpreting the technical scope (Article 70(3)).

II. The "All Elements Rule": The Linchpin of Literal Infringement Analysis

Once the claims have been properly construed, the core test for literal infringement in Japan is the "all elements rule."

A. Definition and Application

For an accused product or process (often referred to as the イ号物件 - Igō Bukken in Japanese litigation) to literally infringe a patent claim, it must contain or satisfy each and every element (構成要件 - kōsei yōken) or limitation recited in that claim.

  • If the accused product/process omits even a single element of the claim, or if one of its features is different from a claimed element (and is not an equivalent, which is assessed under a separate doctrine), then there is no literal infringement of that particular claim.
  • The patentee bears the burden of proving that the accused product/process meets all elements of at least one asserted claim.

B. The Process of Comparison

Determining literal infringement typically involves a methodical comparison:

  1. Claim Construction (Claim Analysis - 分説 - Bunsetsu): The patent claim being asserted is first interpreted to understand the meaning of its terms and scope. It is then conceptually broken down (分説 - bunsetsu) into its individual constituent elements or limitations.
  2. "Articulation" of the Accused Product/Process: The features and characteristics of the accused product or process are clearly identified and described (文章化 - bunshōka) in a manner that allows for a direct, element-by-element comparison with the construed claim.
  3. Element-by-Element Mapping: Each element of the patent claim is compared to the corresponding feature(s) of the accused product/process. Literal infringement is found only if every claimed element has a corresponding identical feature in the accused embodiment.

III. Illustrative Case Law on Literal Infringement in Japan

Japanese courts have applied these principles in numerous cases. Two examples illustrate how claim interpretation and the all elements rule function in practice:

A. Case Study 1: The Kirimochi (Cut Rice Cake) Case – Literal Infringement Affirmed After Reinterpretation of Claim Language

This case involved a patent for a small, generally rectangular piece of mochi (glutinous rice cake) designed for easy and appealing baking, for example, in an oven toaster.

  • Patented Invention: The key feature was the provision of one or more incisions or grooves on the side circumferential surfaces of the mochi (specifically stated in the claim as not being on the placement bottom surface or flat top surface). These side incisions were intended to control the way the mochi puffs up when heated, preventing uncontrolled expansion and resulting in a more desirable shape, like a sandwich.
  • Accused Product: The competitor's mochi also had incisions on its side surfaces. However, it additionally featured cross-shaped incisions on its top surface.
  • The Core Interpretive Issue: The claim language included a phrase to the effect of "...incisions provided on the side circumferential surface... and not on the placement bottom surface or flat top surface..." The dispute centered on whether this phrase meant:
    1. The essential incisions must be on the sides, AND there must not be any incisions on the top/bottom (i.e., a negative limitation prohibiting top/bottom incisions).
    2. The essential incisions must be on the sides, and the "not on top/bottom" part merely emphasizes and clarifies the location of these essential incisions, without necessarily prohibiting additional, different incisions elsewhere.
  • First Instance Decision (Tokyo District Court, November 30, 2010): The District Court adopted the first interpretation, viewing the phrase as a negative limitation. Since the accused product had top incisions, it found no literal infringement.
  • IP High Court Decision (Intermediate Judgment, September 7, 2011): The IP High Court reversed this interpretation. It carefully analyzed the claim language in conjunction with the specification. The court reasoned that the inventive concept lay in the provision of side incisions to achieve the desired puffing effect. The phrase "not on the placement bottom surface or flat top surface" was interpreted as emphasizing the specific location of this inventive feature, distinguishing it from prior art that might have had top/bottom incisions for different purposes. It was not seen as an explicit prohibition against having other types of incisions in addition to the claimed side incisions. Since the accused product possessed the essential side incisions as claimed, the court found that this element was met. Considering other elements as also met, literal infringement was affirmed.
  • Learning Point: This case highlights the critical impact of claim interpretation. The IP High Court focused on the positive recitations of the inventive elements and interpreted potentially limiting language in the context of the overall invention and its purpose as described in the specification. The presence of an additional feature (top incisions) in the accused product did not negate literal infringement because all elements of the claim, as construed, were found in the accused product.

B. Case Study 2: The EZ Assistant Navi Case – Literal Infringement Denied Due to a Mismatched Claim Element

This case concerned a patent for a navigation system where a key claim element was a "vehicle-mounted navigation device" (車載ナビゲーション装置 - shasai nabigēshon sōchi).

  • Accused Product/Service: The defendant offered a mobile phone-based navigation service called "EZ Assistant Navi." This system involved the user's mobile phone communicating with a remote server. While the mobile phone was used within a vehicle during navigation, it was a general-purpose mobile device not permanently installed or primarily dedicated to the vehicle. The server, of course, was not vehicle-mounted.
  • The Core Interpretive Issue: Did the accused system, particularly the user's mobile phone in conjunction with the server, constitute a "vehicle-mounted navigation device" as required by the claim?
  • IP High Court Decision (November 30, 2011): The court interpreted the term "vehicle-mounted navigation device" to mean a device that is physically loaded onto a vehicle and is constantly kept in that state as its primary mode of operation or intended design. It concluded that neither the remote server nor the user's portable, multi-purpose mobile phone met this specific limitation of being "vehicle-mounted" in the claimed sense.
  • Outcome: Because this essential claim element was found to be missing from the accused system, the court ruled that there was no literal infringement.
  • Learning Point: This case underscores the strict application of the "all elements rule." If a specific limitation recited in a claim cannot be found in the accused product or process, literal infringement will be denied. The interpretation of seemingly straightforward terms like "vehicle-mounted" can be decisive.

IV. Nuances and Important Considerations in Literal Infringement Analysis

Several factors add layers of complexity to literal infringement assessments:

  1. Claim Drafting Precision is Paramount: The initial drafting of the patent claims during prosecution is the most critical stage. The choice of words, the breadth or narrowness of terms, and the way elements are combined will fundamentally dictate the scope of literal protection. Ambiguities or unintended limitations introduced during drafting can severely hamper later enforcement efforts.
  2. The Role of the Specification as an Interpretive Guide: As per Article 70(2), the specification and drawings are indispensable tools for understanding the meaning of claim terms. If a term is ambiguous or has a special meaning in the context of the invention, the specification should provide clarification. However, courts are generally cautious about importing limitations from the specification into claims if those limitations are not reflected in the claim language itself. The goal is to interpret the claims, not to re-write them based on preferred embodiments in the specification.
  3. Prosecution History Estoppel (File Wrapper Estoppel - 出願経過禁反言 - Shutsugan Keika Kinhan-gen):
    Statements, arguments, or amendments made by the applicant/patentee during the examination process at the JPO (or during post-grant proceedings like oppositions or invalidation trials) can limit the scope of the claims that can be asserted later. If an applicant, to overcome a rejection or distinguish from prior art, narrows a claim or makes a clear disavowal of certain subject matter, they may be "estopped" from later arguing for an interpretation (either literal or under the doctrine of equivalents) that recaptures that surrendered scope. This doctrine ensures that the public can rely on the patentee's representations made to the JPO.
  4. No "Gist of the Invention" or "Spirit of the Invention" for Literal Infringement:
    Literal infringement analysis in Japan is rigorous and element-focused. It is not sufficient for an accused product to merely capture the "gist" or "spirit" of the patented invention if it does not literally meet all the elements of a claim. The "all elements rule" is strictly applied. (Situations where the "gist" is taken by non-literal means are addressed by the Doctrine of Equivalents, discussed below).
  5. Burden of Proof:
    In a patent infringement lawsuit, the patentee (plaintiff) bears the burden of proving, on a balance of probabilities, that the accused product or process (defendant's activities) falls within the technical scope of at least one of their asserted patent claims. This includes providing evidence to support their proposed claim construction and demonstrating how the accused embodiment meets each claim element.

V. What if There Is No Literal Infringement? The Doctrine of Equivalents

It is important to briefly note that even if an accused product or process does not meet the "all elements rule" for literal infringement, it might still be found to infringe under the Doctrine of Equivalents (均等論 - kintō-ron). This doctrine, recognized by the Japanese Supreme Court (e.g., in the Ball Spline Bearing case, February 24, 1998), allows a finding of infringement if the accused product/process, despite differing from the literal claim language in some insubstantial way, performs substantially the same function in substantially the same way to achieve substantially the same result as the claimed invention, and other specific conditions are met. The Doctrine of Equivalents essentially extends the protective reach of a patent beyond its precise literal wording to prevent trivial evasions. However, this is a distinct analysis from literal infringement.

Conclusion

Determining literal infringement under Japanese patent law is a meticulous process centered on an element-by-element comparison of the patent claims with the accused product or process. The claims, as interpreted in light of the specification and drawings, and potentially limited by the prosecution history, define the legal boundaries of the patentee's exclusive rights. The "all elements rule" stands as a strict gatekeeper: all claimed elements must be present in the accused embodiment for a finding of literal infringement.

For businesses, this underscores the critical importance of precise claim drafting during patent prosecution to capture the true essence of the invention. When asserting a patent, a careful literal infringement analysis is the first step. For those assessing freedom to operate, a detailed comparison against the literal claims of relevant patents is equally crucial to mitigate infringement risks in the Japanese market.