Res Judicata (Kihanki-ryoku) in Japan: What is the Scope and Binding Effect of a Final Civil Judgment?

Japanese Attorney at Law - Bengoshi L.L.

• 10 min read

The principle of "res judicata," Latin for "a matter judged," is a cornerstone of legal systems worldwide, reflecting the fundamental societal interest in the finality of litigation. Once a court has rendered a final and binding judgment on a matter, the same parties should not be permitted to re-litigate that same issue endlessly. In Japan, this crucial doctrine is known as kihanki-ryoku (既判力). Understanding its scope—what is decided, who is bound, and for what period—is essential for appreciating the conclusive power of Japanese civil judgments.

This article provides an in-depth exploration of kihanki-ryoku, detailing its objective, subjective, and temporal scope, its effects, and how it compares to related concepts in common law jurisdictions.

I. Understanding Res Judicata (Kihanki-ryoku) in Japanese Civil Procedure

A. Definition and Rationale

Kihanki-ryoku refers to the binding legal effect of a final and binding (確定 - kakutei) judgment in a civil case. This effect generally precludes the parties to the original lawsuit (and those in privity with them) from subsequently re-litigating the same claim or issue that was, or in some broader interpretations in other systems, could have been, determined in the prior action.

The primary rationales for the doctrine of res judicata are:

  1. Finality of Disputes: To bring an end to litigation over a particular matter, preventing parties from endlessly reopening decided issues (interest reipublicae ut sit finis litium – it is in the public interest that there be an end to litigation).
  2. Legal Stability and Predictability: To ensure that judicial decisions are reliable and can be depended upon by the parties and society.
  3. Judicial Economy: To conserve court resources by preventing the redundant adjudication of the same claims.
  4. Protecting Parties: To protect litigants from the burden and expense of vexatious, repetitive lawsuits concerning matters already decided.

B. Legal Basis: CCP Article 114(1)

The foundational provision for res judicata in Japan is Article 114, Paragraph 1 of the Code of Civil Procedure (CCP) (民事訴訟法 - Minji Soshō Hō):
"A final and binding judgment shall have res judicata effect only with respect to the conclusion of a judicial decision on the claim contained in the main text of the judgment."
(確定判決は、主文に包含するものに限り、既判力を有する。- Kakutei hanketsu wa, shubun ni hōgan suru mono ni kagiri, kihanki-ryoku o yūsuru.)

This article immediately highlights that res judicata in Japan is tied to the "conclusion...on the claim contained in the main text," which directly links its scope to the soshōbutsu (subject matter of litigation).

II. The Objective Scope of Res Judicata (Kakkanteki Han'i): What is Precluded?

The "objective scope" defines what specific matters are covered by the res judicata effect of a judgment.

A. Limited to the "Conclusion on the Claim in the Main Text"

As CCP Article 114(1) clearly states, res judicata attaches only to the court's final determination on the soshōbutsu as expressed in the operative part, or the "main text" (主文 - shubun), of the judgment. The shubun is the dispositive part of the judgment that states the court's order (e.g., "The defendant shall pay the plaintiff JPY X," "The plaintiff's claim is dismissed," or "It is confirmed that the contract between A and B is valid").

  • Dependence on Soshōbutsu Theory: How narrowly or broadly the soshōbutsu itself is defined by Japanese legal theory (predominantly the traditional substantive law theory, which identifies the soshōbutsu with a specific substantive legal right) directly dictates the breadth of the objective scope of res judicata. A narrowly defined soshōbutsu leads to a correspondingly narrow scope of preclusion.

B. No Res Judicata for Reasoning or Incidental Findings

Crucially, the reasons (理由 - riyū) provided by the court in its judgment for reaching the conclusion in the main text, including its findings on specific evidentiary facts or its interpretation of particular legal points en route to the final decision, do not generally acquire res judicata effect in themselves.

  • This means that parties are usually not precluded from re-litigating those specific factual issues or points of law if they arise in a subsequent lawsuit involving a different soshōbutsu, even if those issues were thoroughly discussed in the reasoning of the prior judgment.
  • This is a significant point of distinction from the broader concept of "issue preclusion" or "collateral estoppel" found in common law systems.

C. Exception: Set-Off Defenses (CCP Art. 114(2))

A notable statutory exception to the rule that only the main text judgment on the plaintiff's soshōbutsu has res judicata concerns claims raised by the defendant as a set-off (相殺 - sōsai).

  • CCP Article 114(2) provides: "A judicial decision on the existence or non-existence of a claim raised as a defense of set-off shall have res judicata effect only with respect to the amount of said claim for which set-off was asserted."
  • If a defendant asserts their own claim against the plaintiff as a set-off against the plaintiff's claim, and the court adjudicates the validity and amount of that set-off claim, that part of the judgment does acquire res judicata. This prevents the defendant from re-litigating the existence of that same portion of their claim in a subsequent action.
  • A leading Supreme Court case (Judgment of December 17, 1974, Third Petty Bench, Minshū Vol. 28, No. 10, Page 2038) confirmed that res judicata applies to the court's decision on a set-off claim to the extent it was used for the set-off.

III. The Subjective Scope of Res Judicata (Shukanteki Han'i): Who is Bound?

The "subjective scope" defines who is bound by the res judicata effect of a judgment. This is primarily governed by CCP Article 115, Paragraph 1.

A. Parties to the Litigation (Item (i))

The primary rule is that res judicata binds the persons who were formal parties (plaintiffs and defendants, including intervenors with party status) to the lawsuit in which the judgment was rendered. This reflects the principle of relativity of judgments – a judgment generally only affects the parties to the dispute.

B. Successors After Conclusion of Oral Argument (Item (iii))

Res judicata also extends to those who became successors in interest to a party after the conclusion of oral arguments in the fact-finding instance of the original lawsuit (口頭弁論終結後の承継人 - kōtō benron shūketsu-go no shōkeinin).

  • This ensures that a party cannot evade the effect of an impending or rendered judgment by transferring their rights or obligations related to the soshōbutsu after the evidentiary record has closed.
  • "Successor" can include universal successors (e.g., heirs, a company surviving a merger) or specific successors (e.g., an assignee of the litigated claim, a purchaser of disputed property).

C. Persons Holding the Object of Claim for a Party/Successor (Item (iv))

Res judicata also binds persons who possess the specific object of the claim (e.g., a disputed piece of real estate, a specific chattel) on behalf of a party to the original suit or on behalf of a successor covered by Item (iii). This prevents circumvention of the judgment by transferring possession to a third-party agent or custodian.

D. Persons Represented by Another in Litigation (Item (ii))

When a person litigates as a plaintiff or defendant on behalf of another (e.g., a trustee litigating for a trust beneficiary, an administrator for an estate, a person appointed to conduct litigation for a group), the judgment is also binding on the person whose rights or interests were being represented (the principal, beneficiary, etc.).

E. Extension by Other Specific Laws

In certain types of lawsuits, particularly those involving status or corporate matters, specific statutes may provide that the judgment has a broader effect, sometimes erga omnes (binding against the world) or against all members of a certain group (e.g., all shareholders in an action to nullify a shareholder resolution).

IV. The Temporal Scope of Res Judicata (Jiteki Genkai): When is the Cut-Off?

The "temporal scope" defines the point in time to which the factual and legal situation covered by res judicata is fixed.

A. The Critical Juncture: Conclusion of Oral Argument

Res judicata attaches to the state of the legal relationship or the existence/non-existence of the right (the soshōbutsu) as it existed at the time of the conclusion of oral arguments in the final fact-finding court instance. This is typically the moment when the evidentiary record is closed and the case is ripe for judgment on the facts presented.

B. Post-Cut-Off Events Are Not Precluded

Facts or events that occur after this critical cut-off point, which create new rights or extinguish or modify the rights adjudicated in the prior judgment, are not barred by the res judicata of that prior judgment. Such new facts can be raised as the basis for a new claim or defense in a subsequent lawsuit.

  • Example:
    • Judgment A orders Defendant to pay Plaintiff JPY 1 million. Oral arguments for Judgment A closed on March 1. On March 15, Defendant pays Plaintiff the JPY 1 million. If Plaintiff later attempts to enforce Judgment A, Defendant can raise the post-cut-off payment as a defense in the enforcement proceedings or in a new lawsuit to declare the debt satisfied.
    • If a contract is upheld in Judgment B (oral arguments closed April 1), but a party validly terminates that contract on April 10 due to a subsequently occurring breach, the termination (a new fact) can be asserted in future disputes, despite Judgment B.

It's important to distinguish kihanki-ryoku from related but distinct concepts:

A. Issue Preclusion / Sōtenkō (争点効)

  • As noted, kihanki-ryoku in Japan attaches to the overall soshōbutsu (the claim), not to specific issues or findings within the reasoning of the judgment.
  • However, Japanese courts and scholars have recognized a concept somewhat analogous to common law "issue preclusion" or "collateral estoppel," often referred to as sōtenkō (literally, "issue effect" or "effect of a point in dispute").
  • Sōtenkō suggests that a specific issue of fact or law that was actually and fully litigated by the parties, was essential to the determination of the prior judgment, and was clearly decided by the court, might have a preclusive effect in a subsequent lawsuit between the same parties involving a different soshōbutsu, particularly if re-litigating that same issue would be contrary to the principle of good faith or procedural economy.
  • The legal basis and precise scope of sōtenkō are still subjects of considerable academic debate in Japan, and courts apply it cautiously and under specific conditions. The Supreme Court has issued rulings that show a willingness to consider such effects in limited circumstances where re-litigation of a previously settled key issue would be clearly abusive or inefficient (e.g., Supreme Court, November 24, 1970, Third Petty Bench, Minshū Vol. 24, No. 12, Page 1854, which is often cited in discussions of sōtenkō). It is not as broadly or systematically applied as collateral estoppel in the U.S.

B. Preclusion by the Principle of Good Faith (信義則による遮断効 - Shingi-soku ni yoru Shadankō)

Even if formal res judicata (kihanki-ryoku) or a clear sōtenkō does not apply, a party might be prevented by the overarching Principle of Good Faith and Sincerity in Litigation (CCP Art. 2) from making assertions in a subsequent lawsuit that flagrantly contradict positions they successfully maintained, or facts clearly established, in a prior proceeding between the same parties, if doing so would constitute an abuse of process or be manifestly unfair.

VI. Comparing Japanese Kihanki-ryoku with Common Law Res Judicata/Collateral Estoppel

  • Claim Preclusion (U.S. Res Judicata):
    • The negative effect of Japanese kihanki-ryoku (preventing re-litigation of the same soshōbutsu) is analogous to U.S. claim preclusion. However, a key difference often lies in the scope of what constitutes the "same claim." Because the Japanese soshōbutsu is typically defined more narrowly by the specific substantive legal right asserted (under the traditional theory), it may not preclude as broad a range of related claims as the U.S. "transaction or occurrence" test, which generally bars all claims—whether or not actually litigated—that arose from the same underlying factual nucleus.
  • Issue Preclusion (U.S. Collateral Estoppel):
    • U.S. collateral estoppel is a well-defined doctrine that precludes the re-litigation of specific issues of fact or law that were (1) actually litigated and determined in a prior action, (2) by a valid and final judgment, and (3) where the determination was essential to that prior judgment.
    • Japan's sōtenkō is conceptually similar but is less formally codified, its theoretical underpinnings are more debated, and its application by courts has been more cautious and fact-specific. It is not as robust or systematically applied as U.S. collateral estoppel.

VII. Strategic Implications

  1. Defining the Soshōbutsu is Paramount: The plaintiff's initial framing of the soshōbutsu in their complaint has profound and lasting implications for the scope of res judicata. A narrow framing means narrow preclusion.
  2. Careful Pleading of Set-Offs: Raising a counterclaim as a set-off defense means that the court's decision on that set-off claim will gain res judicata effect (CCP Art. 114(2)). Parties must carefully consider whether it is more advantageous to assert such a claim as a set-off or to pursue it in a separate lawsuit.
  3. Identifying All Necessary Parties: To maximize the useful subjective scope of a favorable judgment, ensure that all parties who should be bound by the decision are properly included in the litigation from the outset or through appropriate joinder or succession mechanisms.
  4. Tracking Post-Oral Argument Developments: Meticulously record any relevant factual changes or events that occur after the conclusion of oral arguments in the fact-finding instance. These new facts are generally not barred by the res judicata of the prior judgment and can be raised in subsequent proceedings.
  5. Assessing Potential "Issue Preclusion" (Sōtenkō): Even when filing a new lawsuit with a technically different soshōbutsu, be aware that findings on crucial, thoroughly contested issues in a prior related case might still, under certain circumstances (especially if re-arguing them seems contrary to good faith), practically influence the subsequent proceedings or be given significant weight by the court.

VIII. Conclusion

Res judicata (kihanki-ryoku) is a fundamental pillar of Japanese civil procedure, embodying the critical principle that litigation must, at some point, come to a definitive end. It ensures the finality and stability of judicial decisions by preventing the same claim (the soshōbutsu) from being re-litigated between the same parties (and their privies) once a judgment becomes final and binding.

Its objective scope is intricately tied to the definition of the soshōbutsu adjudicated in the main text of the judgment, its subjective scope extends primarily to the parties and certain defined successors, and its temporal scope is fixed at the conclusion of oral arguments in the fact-finding instance. While the core concept aims for clarity and preclusion of the decided claim, the nuanced interplay with Japan's soshōbutsu theory and the evolving, though less formalized, considerations of issue preclusion (sōtenkō) mean that a comprehensive understanding of the full preclusive impact of a Japanese judgment requires careful legal analysis. For all litigants, a deep appreciation of kihanki-ryoku is essential for effective long-term legal strategy and for understanding the true finality of a civil judgment in Japan.