[Article / Patents] Adding asserted patent claims during litigation—subject matter of the action and untimely means of attack or defense (森本晃生, Patent, November 2024)
Updated: 8 minutes ago
Article information
Article type: Publication review
Display and classification checked: 2026-09-30
Categories: Patents
Topics: Litigation procedure
Published on this website: 2026-09-29
[Article / Patents] Adding asserted patent claims during litigation—subject matter of the action and untimely means of attack or defense (森本晃生, Patent, November 2024)
The IP High Court reversed the Osaka District Court’s treatment of adding a patent claim as an “amendment of the action” (Code of Civil Procedure, Article 143), holding that it was “submission of a means of attack or defense” (Article 157).
The reason lies in the Patent Act’s basic structure of granting one patent right per patent application.
In an action for infringement of a patent, selecting patent claims is a matter of choosing means of attack supporting a particular subject matter of the action (right of claim).
Thus, adding another claim of the same patent does not change the subject matter or cause of action.
However, the additional argument in this case was dismissed as an untimely means of attack or defense.
Reason 1—Late submission: The defendant had made specific counterarguments on equivalents early, so adding claims as a response could have been considered. Nevertheless, the addition was made suddenly, after the court disclosed its preliminary view of non-fulfillment and after the patentee stated that only a supplementary brief was planned.
Reason 2—Intent or gross negligence: No special circumstances, such as searching foreign literature or a correction-based rejoinder, prevented timely assertion of claims present in the patent from the outset.
Reason 3—Delay in concluding the litigation: The added claims had never been examined. Allowing them would require substantial time to examine new claim construction and requests for clarification of product identification, considerably delaying conclusion.
Practical significance
This IP High Court decision clarified that arguments based on other claims of the same patent constitute the same subject matter of the action.
Under this approach, asserting another claim in a later action is likely to be barred by res judicata, the prohibition of duplicate actions, or the principle of good faith.
It is essential for patentees to assert comprehensively all available claims early, before disclosure of the court’s preliminary view on infringement.
Originally posted on LinkedIn: https://www.linkedin.com/feed/update/urn:li:activity:7510492642435125248/
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Updates and corrections
This log starts on 30 September 2026. Display and classification checks are distinct from a review of the legal analysis.
2026-09-30 — Presentation update: added the article type, this change log and a link to consultation options. The existing article text was preserved.
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