When the Other Side Produces a Document You Say Is Forged｜Challenging the Authenticity of Documentary Evidence in Japan

Midway through the proceedings the other side produces a contract, an acknowledgment of debt or a confirmation letter that appears to settle everything. It bears what looks like your signature, or your company’s seal. You have never seen the document before. At that moment most clients conclude the case is lost. Under Japanese civil procedure it is not. A document does not acquire evidential weight merely by being produced; whether it was genuinely executed by the person whose name it bears is itself a matter that can be contested, and documents are displaced on that ground more often than is generally supposed. What follows is an explanation under Japanese law.

Contents

Authenticity: the presumption arising from a signature or a seal
What to examine when forgery is suspected
The limits of handwriting analysis and seal comparison
Procedures for obtaining what you need
Test the account as a whole, not each document in isolation
In closing
How to contact us

Authenticity: the presumption arising from a signature or a seal

A Japanese court does not go straight to the contents of a document. It must first be satisfied that the document was in fact created by the person named on it — its authenticity, or due execution. For private documents, article 228, paragraph 4 of the Code of Civil Procedure provides that a document is presumed to have been duly executed where it bears the signature or seal of the person concerned or of that person’s agent. Practice has built a second presumption on top of the first, commonly described as the two-stage presumption: where the seal impression on the document matches the party’s own registered or habitual seal, it is presumed as a matter of fact that the seal was affixed by that party’s own volition, and the statutory presumption of authenticity then follows.

Both stages are presumptions, and presumptions can be displaced. The seal may have been kept by someone else; it may have been used without authority, or misappropriated; a seal may have been affixed to a blank sheet which was written up afterwards. Where facts of that kind can be shown well enough to raise a genuine doubt, the first-stage presumption of volition gives way. The point of attack is usually not whether the seal impression is genuine — it very often is — but whether the act of sealing was the party’s own. Keeping those two questions apart is the beginning of a successful challenge.

What to examine when forgery is suspected

Consistency of the date with the paper, the form and the seal. Was that letterhead or that form of contract in use at the date the document bears? Had the seal been carved by then, and was it later recut? Do the company name, the address and the telephone number appear in the style used at the time, as shown on business cards and correspondence of the same period?
The history of custody. Why is a document of such importance produced only now? Where is the original? Who held it, and how? A vague account of custody is itself a mark against the document.
Inconsistency with other evidence. Compare the document against the email, faxes, accounting records, remittance records and diaries of the same period.
Conflict with the facts as they then stood. Was the signatory in the country on that date? Did the job title on the document exist at the time? Is the figure proportionate to the scale of dealings then subsisting between the parties?

The limits of handwriting analysis and seal comparison

A client who suspects forgery usually wants an expert examination of the handwriting at once. It is worth understanding what such an examination can and cannot do. Handwriting analysis yields a judgment of probability rather than certainty, different examiners not uncommonly reach different conclusions, and a court will treat an examination commissioned privately by one party with particular reserve. Comparison of seal impressions has a further difficulty: where a document has been produced by copying an existing impression electronically, a formal match is exactly what one would expect, and the comparison may do the challenging party more harm than good.

An expert examination should therefore not be made to carry the case on its own. It works best as corroboration, offered alongside the circumstantial matters described above rather than in place of them.

Procedures for obtaining what you need

The traces of a forgery usually lie in material the challenging party cannot reach unaided. Japanese civil procedure provides several routes.

An order for production of documents (bunsho-teishutsu-meirei). The court may be asked to order the other party or a third person to produce documents in their possession. Requiring production of the original, or of other documents created in the same period, is often decisive. Where a party fails without justification to comply, the court may treat the opposing party’s assertions as to the contents of that document as true.
A commission to send documents (soufu-shokutaku), by which the court requests a bank, a public office or a hospital to send documents it holds.
A commission of inquiry (chousa-shokutaku), by which the court requests a public or private body to investigate and report on a necessary matter.
A bar association inquiry under article 23-2 of the Attorney Act of Japan, by which an attorney, through the bar association to which the attorney belongs, obtains a reply from a public or private institution on a specified point.

Test the account as a whole, not each document in isolation

Fighting each piece of evidence separately rarely succeeds. What works better is to treat the other side’s case as a single narrative and test it for coherence — the sequence of events, the motive, the naturalness of the conduct. Why would this document have been made at that moment? Why is there no trace of anything done under it afterwards? Why was it never mentioned for years? Each inconsistency may be small; accumulated, they unsettle the court’s confidence in the document itself. Saying plainly “this is a forgery” is generally less effective than showing, point by point, what cannot be explained if the other side’s account is accepted.

A word of caution on the criminal side. Clients who suspect forgery often wish to go straight to a criminal complaint. The offence of forgery of a private document has strict requirements, and producing an untrue document in civil proceedings does not of itself necessarily constitute a crime. Threatening criminal consequences in the course of a civil case can rebound on the party who does so, both in the court’s impression and by creating a fresh dispute. The criminal aspect is better assessed carefully, and separately, once the civil evidence has been built up.

In closing

A document that looks decisive is not a reason to give up. Authenticity can be contested, and the presumption can be displaced; what it takes is the patient construction, from limited traces, of the circumstantial facts that make the document impossible to believe. That construction is the lawyer’s work. Instructions and the review of materials can be handled from outside Japan by email and video conference, and we are equally glad to work through the client’s own counsel abroad.

How to contact us

Telephone 03-6435-8418 within Japan, or +81-3-6435-8418 from overseas. Lines are open from 08:00 to 24:00 Japan time, including Saturdays, Sundays and public holidays. Enquiries are also received at any hour through the form on this site.

M&A Partners Law Office LPC　Katsuhiro Tsuchiya, Representative Attorney-at-Law (Tokyo Bar Association, Registration No. 26775)　17F Mori Trust Shiroyama Trust Tower, 4-3-1 Toranomon, Minato-ku, Tokyo, Japan

This article is a general explanation based on the laws and practice of Japan as at August 2026 (Reiwa 8). The outcome of any particular matter depends on its own facts, and no specific result is guaranteed.

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