Family Register (Koseki) Basics for Binational Families in Japan

May 31, 2026 Maternity Prep Navigator Editorial ~18 min read

Japan's family register system — the koseki — is one of the country's most important civil documentation systems, recording births, deaths, marriages, divorces, and adoptions for Japanese nationals. For binational families — where one or both partners are foreign nationals — the system works somewhat differently than many people expect. This guide explains the key points in plain language, without making legal determinations about any specific family's situation.

1. What Is the Koseki (Family Register)?

The basic concept

The koseki is Japan's official civil registration system for family relationships. Each koseki record is associated with a registered domicile address (honseki), which is a designated address in Japan used solely for the purpose of the koseki registration — it does not have to be the family's actual residential address. Each koseki has a head of household (hittousha) — the person designated as the primary registrant — and other family members are recorded on the same register.

What events are recorded

The koseki records births, deaths, marriages, divorces, adoptions, and other changes in family relationships for Japanese nationals. Each event requires a notification (todoke) to the responsible municipal office within a legally required period. Filing deadlines vary by event type; check with the relevant office for current requirements.

Who is covered

The koseki is for Japanese nationals. Foreign nationals are not independent registrants, but when a foreign national has a legal relationship with a Japanese national (as a spouse, or as parent of a Japanese-national child), information about the foreign national is noted on the relevant koseki record. The foreign national's civil status is maintained through their home country's system.

2. How Is a Foreign Spouse Recorded?

Recording on the Japanese spouse's koseki

When a Japanese national marries a foreign national and the marriage is registered in Japan through a marriage notification (kon'in todoke), the foreign spouse is recorded on the Japanese national's koseki. Specifically, the foreign spouse appears as the spouse of the hittousha (head of household) — but the foreign spouse does not have their own independent koseki entry or page. Their information is referenced within the Japanese spouse's record.

What information about the foreign spouse appears

The following types of information about the foreign spouse are typically recorded on the koseki:

• Name (in katakana — the koseki does not usually record the original-script spelling)
• Date of birth
• Nationality
• Relationship to the head of household (i.e., spouse)

The exact format and what specific information appears may vary depending on the municipal office, the information provided at the time of registration, and the type of koseki extract requested. If accuracy of the recorded information is important to you — for example, if the koseki will be used as evidence of family status in another country — verify the recorded details directly with the municipal office.

Two foreign nationals

If both spouses are foreign nationals — for example, if neither holds Japanese nationality — neither will have a koseki. In this case, family relationships are generally documented through other means: residence registration records (juuminhyou), home country civil certificates, or documents issued for official administrative purposes by local authorities in Japan. The administrative handling of such situations varies; consult your local municipal office or a qualified specialist for guidance specific to your situation.

3. How Are Children of Binational Couples Recorded?

Children who acquire Japanese nationality

A child born to a binational couple — where at least one parent is a Japanese national — may acquire Japanese nationality at birth. When a child acquires Japanese nationality, a birth notification (shusshou todoke) is filed with the municipal office, and the child is entered into the Japanese parent's koseki. The child's name, date of birth, sex, and parentage are recorded there.

Whether a child automatically acquires Japanese nationality depends on factors including the parents' nationalities, whether the parents are married, and other circumstances. For guidance on nationality acquisition and birth registration, see Birth Registration in Japan for Binational Families.

Children born in wedlock (chakushutsushi)

A child born to a married couple (chakushutsushi) is entered into the Japanese parent's koseki when the birth is registered. The child's relationship to both parents is recorded.

Children born outside marriage and recognition (ninchi)

A child born outside of marriage where one parent is Japanese may initially be recorded only under that parent's koseki. If the other parent later recognizes (ninchi) the child — voluntarily (nin'i ninchi) or through a court order (kyousei ninchi) — the recognition is noted on the koseki. The exact recording depends on circumstances and nationalities. This area involves legal complexities; consult a specialist if applicable.

Children who do not acquire Japanese nationality

If a child does not acquire Japanese nationality — for example, because neither parent is Japanese, or because the child acquires only the foreign parent's nationality — the child will not have a koseki. Family relationships are documented through other means, such as the foreign national's home country civil registration, residence records in Japan, and documents issued by the relevant consulate or embassy. For guidance on residence status for your child in Japan, see Dependent Visa & Residence Status for Your Newborn in Japan.

4. How Are Foreign Names Recorded in the Koseki?

Katakana transcription

Foreign nationals' names in the koseki are recorded in katakana — Japan's phonetic script for foreign words. The transcription is based on the pronunciation declared at registration (typically from the passport). The original-script (Latin-alphabet) spelling is generally not recorded on the koseki itself; it is handled instead on the marriage notification form, the residence record (juuminhyou), and the residence card. Katakana is an approximation: sounds not present in Japanese are rendered using the closest Japanese phonetic equivalent.

Consistency with other documents

When the koseki is used for visa applications, inheritance, or civil registration in another country, the name must match the passport and other identity documents. Discrepancies can complicate administrative processes. If you have concerns about how your name is recorded, verify with the relevant municipal office.

Children's names in the koseki

Children registered in the koseki must have names written in kanji (Chinese characters as used in Japanese) or hiragana/katakana. The rules for kanji that may be used in children's names are governed by a specific list of permitted characters. For binational families, choosing a name that is registrable in Japan as well as appropriate for the child's other country of citizenship can require some research. For detailed guidance on naming rules, see Naming Your Baby in Japan: Rules, Kanji & Options for International Families.

5. Obtaining Certified Copies: Touhon and Shouhon

Types of certified copies

There are two main types of certified copy of a koseki record that can be requested:

• Koseki touhon (戸籍謄本 / 戸籍全部事項証明書): A complete certified copy of the entire koseki record — covering all persons recorded on that register. This is the document typically required when the full household's family relationships need to be evidenced.
• Koseki shouhon (戸籍抄本 / 戸籍個人事項証明書): A certified extract covering only the specified individual's portion of the koseki. This is used when documentation of a single person's family registration details is sufficient.

Where and how to obtain them

Certified copies are issued by the municipal office (shiyakusho or kuyakusho) for the municipality where the registered domicile (honseki) is located — which may differ from where you currently live. Requests can be made in person at the holding office or by mail to that office. Since March 2024, a koseki touhon (full certified copy) can also be obtained in person at any participating municipal office nationwide via the cross-municipality issuance network — but note this network covers only the full copy (touhon), not the individual extract (shouhon), is limited to in-person requests by the registrant or their spouse, direct ascendants, or direct descendants, and is not available by mail or through a proxy. Fees are generally in the range of several hundred yen per copy as of 2026, but vary by municipality and are subject to change. Confirm current fees with the relevant office.

Who can request a certified copy

Persons recorded on the koseki and certain family members can generally request copies. Third parties may do so in specific circumstances. Confirm eligibility with the relevant municipal office if unsure.

6. Using the Koseki Abroad: Translation and Apostille

Translation

The koseki is issued in Japanese. For use abroad, an official translation will typically be required. Requirements for translation — who qualifies as a translator, what certification is needed — vary by country and institution. Check with the specific authority where the document will be submitted. This article does not recommend translation providers.

Apostille certification

Japan is a signatory to the Hague Apostille Convention. For other signatory countries, a koseki document can be certified with an apostille — a standardized certification of the issuing authority's authenticity. In Japan, apostilles for civil documents are issued by the Ministry of Foreign Affairs (Gaimushou). Submit the original certified koseki copy to the relevant Ministry of Foreign Affairs office. Procedures and times vary; confirm current procedures with the Ministry directly.

If the destination country is not an Apostille Convention signatory, consular or embassy legalization may be required instead. Check with the relevant consulate or embassy.

Order of translation and apostille

Some authorities require both translation and apostille, with specific requirements about the order (apostille the original first, then translate; or translate first, etc.). Requirements vary by destination country and institution. Confirm before proceeding.

7. FAQ

Does my foreign spouse get their own koseki?

No. Foreign nationals do not have their own independent koseki. When a foreign national marries a Japanese national and registers the marriage in Japan, the foreign spouse is recorded on the Japanese spouse's koseki as a referenced entry — not as a separate registrant. Their civil status remains in their home country's registration system.

Is the foreign spouse's name written in Japanese characters?

The name is recorded in katakana (Japanese phonetic script), based on the pronunciation declared at registration. The original-script spelling is generally not recorded on the koseki itself (katakana only) — it is handled on the marriage notification form, the residence record (juuminhyou), and the residence card. Katakana is an approximation of the original pronunciation using Japanese phonetics.

If our child has both Japanese and foreign nationality, are they in the koseki?

Yes. A child who acquires Japanese nationality is entered into the Japanese parent's koseki through birth registration. Dual nationality does not prevent koseki entry. For guidance on birth registration and nationality, see Birth Registration in Japan for Binational Families.

Where is our koseki kept?

The koseki is held by the municipal office (shiyakusho or kuyakusho) for the registered domicile (honseki) municipality — which does not have to be where you currently live. Certified copies are obtained from that office, or through the cross-municipality issuance network at participating offices.

How long does it take to get a certified copy?

In-person applications at the holding municipal office are generally processed the same day. Mail applications take longer. For time-sensitive needs (visa applications, etc.), apply in person where possible. Confirm current processing times with the relevant office.

I need the koseki for use in my home country. What do I need to do?

General steps: (1) obtain a certified copy (koseki touhon or koseki shouhon) from the municipal office; (2) arrange an official translation; (3) if your home country requires apostille, obtain one from the Japanese Ministry of Foreign Affairs; (4) check for any additional requirements (legalization, notarization, etc.) with the specific authority receiving the document. Requirements vary by country and institution — confirm before proceeding.

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