How to Search Japanese Patents: Reading Tokkai and Tokkyo Numbers, and Finding English Publications
Checked: 2026-09-21. J-PlatPat changes its screens periodically, so the labels below are the labels verified for this guide. The most important rule is simple: a Japanese application number, publication number and grant number are related records, not interchangeable identifiers.
1. Identify the Japanese document before searching
- `特願` is an application number. A current-looking example is `特願2022-017525`. It identifies the case filed at the JPO; it is not itself the published patent document.
- `特開` is a published unexamined patent application. The familiar local form is `特開2017-165727`; the corresponding DOCDB-style publication is `JP2017165727A`. The four-digit year is followed by a serial number, and `A` is the publication kind used by the source record.
- `特表` is a national publication of a PCT application, usually printed as `特表2024-500123` (year plus serial). It is a Japanese publication of the national-phase translated material, not the same identifier as the WO application. Confirm the exact kind code in the database record instead of manufacturing one from the printed label.
- `特許` is a granted patent registration, such as `特許7324431`. In DOCDB sources it is commonly represented with a grant kind such as `JP7324431B2`; the full kind code matters.
- Utility models use separate `実開`/`実用新案登録` labels and the source kind codes `U` or `Y`. Do not turn a utility-model registration into a patent `A` or `B` number merely because the digit count looks similar.
The JPO relationship is easiest to see in one real result: J-PlatPat can show `特願2004-106468` as the application number, `特開2005-287741` as the publication number, and `特許4182222` as the registration number. They belong to one prosecution history, but each is a different search key and a different document version.
2. Japanese eras and external number formats
`特開平11-297662` means Heisei 11, which is 1999, and DownloadPatent normalizes it to `JPH11297662A`. A modern example, `特開2017-165727`, uses the Western year and resolves to `JP2017165727A`. Reiwa 4 is 2022, but converting an era year to a Western year and then deleting the era marker is unsafe: the serial sequence and the source's document kind still have to be preserved.
The J-PlatPat number inquiry accepts the office's era-style input such as `H11-297662`, and its current help says that hyphens and leading zeros may be omitted. Full-width and half-width characters are accepted, and multiple numbers can be separated by spaces. That tolerance is useful for manual searching; it does not mean every downstream source accepts the same spelling.
Google Patents and Espacenet use a DOCDB-like identifier without spaces, for example `JP2017165727A`. Era records are a special case: DownloadPatent keeps the `JPH`/`JPS` form, while some services' URLs remove a leading zero from an era serial. Preserve both the identifier you searched and the exact source identifier in an audit note. A seven-digit number without a kind marker is also ambiguous between a patent grant and a utility-model registration; do not guess.
3. Match the number to the system's input field
J-PlatPat's known-number workflow is document-oriented. Its result can expose fields named `出願番号` (application number), `公開番号` (publication number) and `登録番号` (registration number). Taiwan's GPSS keeps publication numbers and application numbers in separate search fields as well. A GPSS record is bibliographic data, not a specification PDF.
Espacenet's publication-number search expects a standardized publication identifier such as `JP2017165727A`. PATENTSCOPE exposes fields such as `Application Id/Number`, `Offices`, `Languages` and `ID/Number`; it is especially useful for WO records and participating national or regional collections. If the only number in your file is `特願2022-017525`, first resolve it to the publication or registration record; do not paste the application digits into a publication-number field and assume that the result is the same case.
4. Search manually in J-PlatPat
For a known number, open J-PlatPat and choose `特許・実用新案番号照会／OPD`. Set `検索対象` to `文献`, choose `入力種別` as `番号入力`, select the issuing country or office `日本(JP)`, then choose the matching `文献種別` such as `公開番号・公表番号(A)` or the application/registration option. Enter `2017-165727` for the `特開` example, run the search, and open the `公開番号` result. You can also enter the local notation `特開2017-165727` when the screen accepts it.
On the result page, check the displayed `出願番号`, `公開番号`, `登録番号`, title, applicant, inventor and publication date before downloading or citing anything. The document tabs may include `書誌`, `要約`, `請求の範囲`, `詳細な説明` and `図面`. If you are searching by words rather than a known number, use `特許・実用新案検索` and the detailed search service. The simple search is intentionally limited and should not be treated as an exhaustive prior-art search.
This manual route is valuable even when an automated resolver is available: it tells you whether you started with the wrong number type, whether the case has a publication at all, and whether the PDF shown by J-PlatPat is a publication, a register document or only a bibliographic hit.
5. Where to obtain an English publication
First inspect the Japanese record's family in Espacenet. The family pane may list `Also published as` members. Choose an EP, US or WO family publication whose priority relationship and technical scope match the Japanese document, then download that member's original publication. It is a separate publication, not an official English translation of the Japanese PDF. A simple-family match can also omit an important continuation, divisional or national-phase distinction, so record the member number and priority data.
PATENTSCOPE is the second place to check, particularly when the Japanese case is related to a PCT filing. It can expose PCT full text and documents from participating offices, and its `Documents` area may offer an English machine-translated version of Japanese material. The labels `Application Id/Number`, `Offices` and `Languages` help narrow the result. WIPO Translate is a reading aid; machine translation has no legal force and should not be cited as an official English publication for claim interpretation.
The difference matters in US and EP work. An English family member has its own publication date, claims and amendments. A machine translation has the source document's identity but translated wording. An official English text, where an office actually issued one, is a third category. Keep the Japanese original, family member and translation as separate records rather than renaming one as another.
6. Why a bibliographic hit can have no PDF
There are several normal failure modes:
- GPSS can return publication and application numbers, a title and classification data without a specification or drawings file. A bibliographic record does not replace a document source.
- A Japanese PDF can be missing from one service and present in another: Google Patents may have no PDF link; Espacenet may be busy or unable to provide that document. For JP, Espacenet commonly provides an image-only PDF rather than searchable text.
- The result may be an application that has no published document, a grant with the wrong `B1`/`B2` kind, or an era identifier whose external URL spelling differs. A source can therefore have the right family metadata but fail the exact-document lookup.
- A response that looks like a PDF can be an HTML error page or a partial file. DownloadPatent checks the file and reports a failure instead of keeping a corrupt file.
When this happens, copy the exact `公開番号` or `登録番号` and kind code from J-PlatPat, check the same number in Google Patents and Espacenet, and keep the bibliographic record even if the file remains unavailable. Search success is not retrieval proof. If you need the English version, check the family member or PATENTSCOPE separately; it is not evidence that the Japanese PDF itself exists.
DownloadPatent follows these same distinctions: paste the supported Japanese number, review the resolved document and kind, and treat any English family publication as an optional, separately identified result rather than as a replacement for the original.