Amending, Dividing, or Claiming Internal Priority for Japanese Patent Applications: What Are the Rules and Limitations?

Japanese Attorney at Law - Bengoshi L.L.

• 8 min read

Navigating the patent prosecution process in Japan involves several key procedural tools that allow applicants to refine their applications, manage complex inventions, and incorporate later developments while striving to maintain the benefit of an early filing date. Understanding the rules and limitations surrounding amendments, divisional applications, and domestic priority claims is crucial for effectively prosecuting patent applications before the Japan Patent Office (JPO). These mechanisms provide flexibility but are governed by strict regulations, primarily to ensure fairness to third parties and uphold the integrity of the patent system, particularly the first-to-file principle and the prohibition against adding new subject matter after filing.

I. Amendments (Hosei): Refining Your Patent Application During Prosecution

An amendment allows an applicant to modify the specification, patent claims, or drawings of a pending patent application. Such modifications are often made to correct deficiencies, clarify the invention, or, most commonly, to distinguish the invention from prior art cited by an examiner during the substantive examination phase. When an amendment is properly made, its effect is generally retroactive to the original filing date of the application.

Common Scenarios for Amendments

A frequent use of amendments is to overcome rejections based on lack of novelty or inventive step. For example, if an initial claim is to a broad concept like a "flat panel display," and the examiner cites prior art showing certain types of flat panel displays (e.g., LCDs), the applicant might amend the claim to a narrower scope, such as a "plasma display panel," if the original disclosure supports such a distinction and the narrower scope is patentable over the art.

Crucial Limitations on Amendments

While amendments offer flexibility, they are subject to significant restrictions regarding both timing and substance, as primarily set forth in Article 17-2 of the Japanese Patent Act.

A. Timing Restrictions

An applicant does not have an unfettered right to amend at any point during prosecution. The permissible windows for filing amendments are generally:

  • Before the JPO issues the first office action (typically, during the period for requesting examination).
  • Within the designated period for responding to an office action from the JPO (e.g., an initial notice of reasons for rejection).
  • Within the designated period for responding to a final notice of reasons for rejection.
  • At the time of filing an appeal against a final decision of rejection (the amendment must be submitted simultaneously with the request for appeal).

B. Substantive Restrictions

Several substantive limitations govern the content of amendments:

  1. The Cardinal Rule: No New Matter (Shinki Jikō no Tsuika Kinshi)
    This is the most fundamental restriction, applicable at all stages of amendment (Article 17-2(3)). Any amendment to the specification, claims, or drawings must remain within the scope of the matters disclosed in these documents as originally filed (tōsho meisai-sho tō).
    The rationale is to prevent an applicant from introducing what is effectively a new invention after the original filing date, which would undermine the first-to-file principle and the requirement that the invention be fully disclosed at the time of filing.
    The test for new matter is whether the amended subject matter introduces new technical information that a person skilled in the art would not have directly and unambiguously derived from the totality of the original disclosure. For example, if an original application disclosed "bean paste" generally and discussed its non-freezing properties when refrigerated, an amendment to claim "bean paste specifically for ice cream" might be considered new matter if the "for ice cream" application was not disclosed or directly and unambiguously derivable from the original specification.
  2. Unity of Invention for Amendments After a First Office Action (Shift Amendment Prohibition)
    After an applicant has received a first office action responding to reasons for rejection, any amendment to the patent claims cannot change the invention to one that lacks unity of invention (as defined in Article 37) with the invention(s) that were examined leading to that office action (Article 17-2(4)).
    This rule, sometimes called the prohibition of "shift amendments," prevents applicants from essentially obtaining examination of a different inventive concept within the same application after an initial examination has already been conducted. For example, if an application initially claimed a "high-sensitivity antenna for mobile phones" and, after receiving a rejection on this claim, the applicant attempted to amend the claim to a "hinge for foldable mobile phones" (even if hinges were mentioned in the original specification), such an amendment would be disallowed if the antenna and hinge inventions lack unity. This rule was introduced to ensure fairness and examination efficiency.
  3. Restricted Purposes for Late-Stage Amendments
    For amendments made after receiving a final notice of reasons for rejection, or when filing an appeal against a final decision of rejection, the permissible purposes for amending the claims are strictly limited (Article 17-2(5)). These purposes are:
    • Deletion of a claim(s).
    • Restriction of the scope of a claim (i.e., narrowing the claim).
    • Correction of errors (e.g., typographical errors).
    • Clarification of an ambiguous description (where the ambiguity was noted by the examiner).
      This limitation aims to streamline the examination process at its concluding stages, ensuring that amendments do not necessitate a completely new search or examination.
  4. Independent Patentability for Certain Late-Stage Narrowing Amendments
    If an amendment made after a final rejection or when filing an appeal is for the purpose of restricting the scope of a claim (narrowing), the invention as defined by the amended claim must be independently patentable (Article 17-2(6)). This means the narrowed claim, on its own, must satisfy requirements such as novelty and inventive step.

C. Consequences of Non-Compliant Amendments

  • If an amendment introduces new matter before a final rejection is issued, this typically becomes a new ground for rejection, and the applicant will be notified. The applicant may then have an opportunity to file a further corrective amendment.
  • If an amendment filed after a final notice of reasons for rejection does not comply with the applicable restrictions (e.g., introduces new matter or is for an impermissible purpose), the examiner will issue a decision to dismiss the amendment, and the prior rejection is likely to be made final.
  • Crucially, if a patent is inadvertently granted with an amendment that included new matter, this constitutes a ground for subsequent invalidation of the patent (Article 123(1)(i)).

II. Divisional Applications (Bunkatsu Shutsugan): Pursuing Separate Aspects of Your Invention

A divisional application, provided for under Article 44 of the Patent Act, allows an applicant who has filed a patent application containing two or more inventions (the "parent" or "original" application) to separate one or more of these inventions into one or more new, distinct patent applications.

Purpose and Key Benefit

The most significant benefit of a divisional application is that it is generally deemed to have been filed on the same date as the original parent application (Article 44(2)). This means it retains the parent's crucial filing date for the purpose of assessing novelty, inventive step, and other prior art-related conditions (though certain exceptions apply ). This mechanism allows applicants to pursue protection for different facets of their initial disclosure without losing their priority date.

Common Use Cases for Divisional Applications

  1. Overcoming Lack of Unity Rejections: If an examiner finds that an application contains multiple inventions that do not meet the requirements for unity of invention (Article 37), the applicant can file one or more divisional applications for the non-unified inventions. The parent application is then typically amended to remove the claims directed to the divided-out inventions.
  2. Claiming Disclosed but Initially Unclaimed Subject Matter: Applicants may disclose more in their initial specification and drawings than they initially claim. A divisional application can be used to pursue patent protection for such subject matter that was part of the original disclosure but not included in the original claims. The Supreme Court of Japan has affirmed that such disclosed-but-unclaimed subject matter can validly form the basis of a divisional application, provided the original disclosure was enabling for that subject matter (Supreme Court, December 18, 1980; Supreme Court, March 13, 1981).

Requirements for a Valid Divisional Application

  • Applicant: The applicant for the divisional application must be the same as the applicant for the parent application.
  • Timing: Divisional applications can only be filed during specific windows (Article 44(1)):
    • During the time when amendments to the specification, claims, or drawings of the parent application are permissible.
    • Within three months from the date of receiving a decision of rejection for the parent application.
    • Within 30 days from the date of receiving a decision to grant a patent for the parent application (this allows for division even after allowance to pursue, for example, narrower claims or different aspects).
  • Content:
    • The divisional application must conceptually derive from "part" of the inventions disclosed in the parent application. In practice, this means the divisional application cannot be an exact duplicate of the parent.
    • Crucially, the specification, claims, and drawings of the divisional application must not contain any new matter beyond what was disclosed in the parent application as originally filed. This is a strict requirement, analogous to the no-new-matter rule for amendments.

Flexibility of Divisional Applications

Compared to late-stage amendments in a parent application, divisional applications offer more flexibility regarding the purpose of claim changes. As long as no new matter is introduced, an applicant can file a divisional application with claims that might not have been permissible as a late-stage amendment in the parent (e.g., due to the restricted purposes under Article 17-2(5)). This is because a divisional application is treated as a new, separate application (requiring new fees), and its examination does not necessarily delay or complicate the concluding stages of the parent application's prosecution in the same way a substantial late-stage amendment to the parent might.

III. Domestic Priority Rights (Kokunai Yūsengen): Incorporating Improvements and Later Developments

The domestic priority system in Japan (Article 41 of the Patent Act) allows an applicant who has already filed a patent application in Japan (the "earlier application" or "priority application") to file a subsequent, more comprehensive application (the "later application") within one year from the filing date of the earlier application, while claiming the benefit of the earlier application's filing date for commonly disclosed subject matter.

Purpose and Mechanism

This system is particularly useful when an applicant makes further developments, improvements, or obtains additional supporting data related to an invention shortly after an initial filing. Instead of filing multiple separate applications or attempting potentially problematic amendments, they can consolidate this into a single, updated "later application" that claims domestic priority.

Upon a valid domestic priority claim, the earlier application is deemed withdrawn after a statutorily prescribed period (e.g., 1 year and 3 months from its filing, or as determined by Ministry of Economy, Trade and Industry (METI) ordinance following a 2014 amendment) (Article 42(1)). The later application then proceeds through examination.

Consider an applicant who files an application for a basic invention "A". Within the following year, they develop an improvement "A'" and gather additional experimental data. They can then file a "later application" disclosing and claiming A, A', and the new data, while claiming domestic priority from the application for A.

Effect of the Domestic Priority Claim

The effect of the priority claim is governed by Article 41(2):

  • For any subject matter claimed in the later application that was already disclosed in the specification, claims, or drawings of the earlier application as originally filed, the filing date of the earlier application will be recognized for the purpose of determining patentability conditions like novelty and inventive step over prior art.
  • For any subject matter introduced in the later application that was not disclosed in the earlier application (e.g., the improvement A' or the new data), the priority benefit does not extend. This "new matter" will be assessed for patentability based on the actual filing date of the later application.

Determining the Scope of Priority Benefit

A critical aspect is determining precisely what subject matter in the later application is entitled to the earlier filing date. This involves comparing the technical matters claimed in the later application with the technical matters disclosed in the entirety of the original documents of the earlier application. If a technical matter in a claim of the later application exceeds the scope of disclosure in the earlier application, that specific part of the claim does not receive the benefit of priority. A Tokyo High Court decision on October 8, 2003 (concerning an artificial nipple invention) elaborated on this comparison, emphasizing that the technical matter of the later claim must be within the scope of technical matters disclosed in the earlier application's original documents for priority to apply.

Conclusion

Amendments, divisional applications, and domestic priority claims are indispensable tools in the Japanese patent prosecution toolkit. They provide applicants with valuable mechanisms to refine claims in response to examination, pursue distinct inventive concepts from a single initial disclosure, and incorporate subsequent developments into their patent strategy while preserving early effective filing dates for originally disclosed content. However, these flexibilities are counterbalanced by strict rules, most notably the overarching prohibition against introducing new matter. A thorough understanding of these provisions, their requirements, and their strategic implications is essential for optimizing patent protection in Japan.