Can I Change My Claim Mid-Lawsuit in Japan? Requirements and Effects of Amending a Claim

Japanese Attorney at Law - Bengoshi L.L.

31 May 2025 • 9 min read

Litigation is a dynamic process. As a case unfolds, new facts may come to light, legal strategies may evolve, or the underlying circumstances of the dispute itself might change. In Japanese civil procedure, a plaintiff is not necessarily locked into the precise claim they initially filed. The Code of Civil Procedure (CCP) provides a mechanism for "amendment of a claim" (uttae no henkō), allowing a plaintiff to modify their lawsuit while it is pending. This procedural tool aims to strike a balance between providing plaintiffs with the flexibility to adapt their case and protecting defendants from unfair surprise or undue procedural burdens, all while ensuring the efficient administration of justice.

The Nature and Purpose of Amending a Claim

An amendment of a claim, as governed by Article 143 of the CCP, refers to an alteration made by the plaintiff to the core components of their lawsuit after it has been initiated. This can involve changing the specific relief sought from the court (e.g., changing a demand for specific performance to a demand for monetary damages) or modifying the factual or legal grounds upon which the claim is based (the "cause of action"). The key characteristic is that these changes occur within the framework of the existing, ongoing lawsuit, rather than requiring the plaintiff to start anew with a separate action.

The rationale for allowing such amendments is multifaceted:

Procedural Economy: It is generally more efficient to address related aspects of a dispute within a single proceeding rather than compelling parties to initiate multiple, potentially overlapping, lawsuits. Amending an existing claim can leverage the procedural progress already made.
Fairness to the Plaintiff: Litigation can be a journey of discovery. Facts or legal arguments that were not apparent at the outset might emerge as the case develops. Allowing amendments gives the plaintiff an opportunity to adjust their claim to reflect this evolving understanding, ensuring they can seek the most appropriate remedy.
Comprehensive Dispute Resolution: By permitting amendments, the legal system encourages the resolution of the entire underlying dispute between the parties in one consolidated action, rather than fragmenting it into several pieces.

However, this flexibility is not unfettered. The CCP imposes specific requirements to ensure that the amendment process is not abused and does not unduly prejudice the defendant or impede the swift administration of justice.

Key Requirements for Amending a Claim (CCP Article 143(1))

Article 143(1) of the CCP lays down the primary conditions for the permissibility of an amendment of a claim. The amendment must be made before the conclusion of oral argument in a fact-finding instance (typically the District Court, or the High Court when it acts as the first instance for fact-finding). Crucially, two substantive requirements must be met:

No Change to the Basis of the Claim (請求の基礎に変更がないこと - Seikyū no Kiso ni Henkō ga nai Koto): This is often translated as "identity of the basis of the claim." It means that the amended claim must remain sufficiently connected to, or share a common foundation with, the original claim. The purpose of this requirement is to protect the defendant from being forced to defend against an entirely new and unrelated dispute suddenly injected into the existing lawsuit, which would constitute unfair surprise and could render their prior defensive efforts moot.The precise meaning of "basis of the claim" has been subject to considerable academic and judicial interpretation. Generally, it is understood to involve:It's often suggested that as litigation progresses and more materials are accumulated, the emphasis in assessing this "identity" may gradually shift from a purely substantive factual link to also considering the procedural continuity and the reusability of existing litigation materials. If this fundamental requirement of a common basis is not met, the amendment is generally not permitted unless the defendant consents to it. If the defendant proceeds to argue the merits of the amended claim without objecting to the lack of a common basis, their consent may be implied.
- Substantive/Factual Connection: Courts often look to whether the underlying factual dispute, the societal or economic interests at stake, or the core "life event" giving rise to both the original and amended claims are substantially the same. If the new claim arises from a completely different set of historical facts or transactions, this requirement is unlikely to be met.
- Procedural/Evidentiary Connection: Another perspective considers whether the evidence, arguments, and other litigation materials already presented or developed in connection with the original claim can be substantially utilized for the adjudication of the amended claim. If the amendment would necessitate an entirely new line of factual inquiry and evidence, making the prior proceedings largely irrelevant, the connection might be deemed insufficient.
Not Causing Significant Delay to the Proceedings (著しく訴訟手続を遅滞させることとならないこと - Ichijirushiku Soshō Tetsuzuki o Chien Saseru Koto to naranai Koto): Even if the amended claim shares a common basis with the original, it will not be permitted if it is likely to cause "significant delay" to the overall conclusion of the litigation. This requirement serves the public interest in judicial efficiency and the timely resolution of disputes.The court assesses this ex officio (on its own initiative). The defendant's consent to an amendment that otherwise meets the "common basis" requirement cannot override this condition if the court determines that the amendment would indeed lead to an unacceptable delay. What constitutes "significant delay" is a matter of judicial discretion, depending on the stage of the proceedings, the nature of the amendment, and the extent of new evidence or arguments it would entail. For example, an amendment proposed very late in the proceedings, after extensive evidence has already been examined and the case is nearing readiness for judgment, is more likely to be seen as causing significant delay if it requires reopening major factual inquiries. Legal commentaries note that even if an amendment is disallowed on grounds of potential delay, the plaintiff often retains the right to file a separate lawsuit for the new claim, which raises an interesting point about whether disallowing the amendment in the existing suit truly serves overall judicial economy in every instance, or merely shifts the burden to a new proceeding.

Types of Claim Amendments

Amendments to a claim can generally take one of two forms:

Additional Amendment (追加的変更 - Tsuika-teki Henkō): In this scenario, the plaintiff maintains their original claim but adds a new, related claim to be adjudicated concurrently within the same lawsuit. For example, a plaintiff who initially sued for the delivery of goods under a contract might later add a claim for damages resulting from the delayed delivery of those same goods. Both claims would then proceed together.
Substitutive (or Exchange) Amendment (交換的変更 - Kōkan-teki Henkō): Here, the plaintiff effectively withdraws their original claim and replaces it with a new one. For instance, if a plaintiff initially seeks specific performance of a contract (e.g., the transfer of a unique item), but the item is subsequently destroyed, they might amend their claim to seek monetary damages for breach of contract instead, abandoning the claim for specific performance.

The theoretical nature of substitutive amendments has been a point of discussion in Japanese procedural law.

One view, known as the Composite Act Theory (複合行為説 - fukugō kōi setsu), treats a substitutive amendment as a combination of two distinct procedural acts: (a) an additional amendment to introduce the new claim, and (b) a withdrawal of the original claim. A Supreme Court of Japan decision of February 28, 1957 (Minshu Vol. 11, No. 2, p. 374), is often seen as aligning with this perspective. If this theory is strictly applied, and if the defendant has already substantively responded to the original claim, the withdrawal component would require the defendant's consent under CCP Article 261(2). The Supreme Court later indicated (decision of January 21, 1966, Minshu Vol. 20, No. 1, p. 94) that if a defendant responds to the merits of the new claim without objecting to the substitution, their consent to the withdrawal of the old claim might be implied.
Another view, the Unique Type Theory (独自類型説 - dokuji ruikei setsu), argues that a substitutive amendment is a singular, distinct procedural act with its own characteristics, not merely a joinder and withdrawal. Scholars favoring this view often do so to provide a more coherent explanation for certain effects, such as the continuation of the interruption of the statute of limitations (which originally attached to the filing of the old claim) for the new claim, and the seamless carry-over of litigation materials from the old claim to the new. However, even many proponents of this theory acknowledge the need to protect the defendant's interests, often arguing by analogy to CCP Article 261(2) that the defendant's consent should still be required if they have already substantively engaged with the original claim.

In practice, regardless of the precise theoretical construction, if a plaintiff seeks to entirely replace an old claim with a new one after the defendant has substantially engaged with the old claim, the defendant's consent (or at least their failure to object when given the opportunity) is generally considered necessary for the effective removal of the original claim from the court's consideration.

Effects of a Permitted Amendment

When a court permits an amendment of a claim, several important procedural consequences follow:

Continuation of the Lawsuit: The existing lawsuit continues, now incorporating the amended claim(s). A new lawsuit does not need to be filed.
Utilization of Prior Proceedings: Generally, pleadings, evidence, and other litigation materials submitted before the amendment can be utilized for the purposes of adjudicating the amended claim, especially where the "identity of the basis of the claim" is strong. This promotes efficiency by avoiding the need to re-submit or re-examine materials relevant to both the old and new aspects of the claim.
Interruption of the Statute of Limitations (Jikō no Chūdan): This is a particularly significant effect. If an amendment is properly made and accepted by the court, the interruption of the statute of limitations that was achieved by the filing of the original complaint is generally considered to extend to the amended claim. This means that for limitation purposes, the amended claim is treated as if it were filed at the time of the original complaint, provided the "identity of the basis of the claim" is maintained. This can be a crucial advantage, especially if the statute of limitations for the new aspect of the claim would have otherwise expired.

The Amendment Procedure

A plaintiff wishing to amend their claim typically files a written motion with the court (CCP Article 143(2)). This motion should clearly indicate the proposed changes to the relief sought and/or the cause of action. The court will then rule on the permissibility of the amendment, taking into account the statutory requirements (identity of basis, no significant delay) and often after giving the defendant an opportunity to state their opinion on the proposed amendment.

Illustrative Scenario: From Specific Performance to Damages

Consider a scenario (similar to one outlined in legal commentaries ): A plaintiff (X) sues a defendant (Y) for the specific performance of a contract for the sale of a unique house, demanding delivery of the house and transfer of title registration. The validity of the sales contract is disputed by Y. After the issues have been somewhat clarified in preparatory proceedings, but before the main evidence examination on the contract's validity, the house is destroyed by an accidental fire. X now wishes to amend the claim to seek monetary damages from Y, alleging that the destruction was due to Y's negligence (making performance impossible).

In analyzing the permissibility of this amendment:

Identity of the Basis of the Claim: The underlying sales contract and its disputed validity are central to both the original claim for specific performance and the new claim for damages due to non-performance of that same contract. The core factual and legal nexus (the alleged contractual relationship and its breach) is substantially the same. Therefore, this requirement would likely be met.
Significant Delay: This would be a key consideration. If the litigation was already well-advanced on the issue of the contract's validity, and if the new claim for damages due to Y's alleged fault in the fire requires extensive new evidence on the cause of the fire, Y's negligence, and the quantum of damages, the court would have to assess whether this shift constitutes "significant delay." If the prior work on contract validity is still highly relevant to the damages claim (as it likely would be, since a valid contract is a prerequisite for damages for its breach), the amendment might be allowed. However, if the case was nearly ripe for judgment on the specific performance claim, and the amendment introduces complex new factual inquiries that would substantially prolong the proceedings, the court might find that it causes undue delay. The fact that specific performance is no longer possible due to the house's destruction would be a strong factor in favor of allowing an amendment to a damages claim, as it reflects a material change in circumstance directly related to the original subject matter.
Type of Amendment: This would be a substitutive amendment, as the claim for delivery of the house is no longer feasible.
Defendant's Consent (for withdrawal of the original claim aspect): If Y had already filed a substantive answer and engaged with the merits of the specific performance claim, Y's consent (or lack of objection to the substitution) would generally be required for the effective "withdrawal" component of this substitutive amendment.

Conclusion

The ability to amend a claim under Article 143 of the Japanese Code of Civil Procedure provides an important avenue for plaintiffs to adapt their lawsuits to evolving circumstances and insights. This procedural flexibility promotes comprehensive dispute resolution and judicial economy by often obviating the need to file entirely new lawsuits. However, this plaintiff-friendly mechanism is carefully balanced by requirements designed to protect the defendant from unfair surprise and to prevent the litigation process from being unduly prolonged or derailed. The core conditions—the "identity of the basis of the claim" and the absence of "significant delay"—are subject to judicial interpretation based on the specific facts and progress of each case. For litigants in Japan, understanding when and how a claim can be amended, and the effects of such an amendment, particularly concerning the statute of limitations and the utilization of prior litigation efforts, is a critical aspect of effective case strategy.