New Japanese Imperial Era: Retrieval of Japanese Patent Information

On 30th April 2019 Emperor Akihito of Japan abdicated and his son Emperor Naruhito acceded to the Chrysanthemum Throne on 1st May.  This marked the end of the Imperial Heisei era and the beginning of the Reiwa era.

In this post I look at how the Japanese Imperial eras define the calendar dates and passage of time in many Japanese documents, including (in previous years) patents and patent applications.

Although the Japanese Patent Office started using Gregorian calendar years in 2000 and no longer uses the Imperial calendar, searching, retrieving and analysing older Japanese patents and applications still requires knowledge of the Imperial calendar system.


A History of the Japanese Patent Numbering System

Many aspects of Japanese society mark time by the Imperial calendar – the eras defined by the reigns of individual emperors.  Japan first adopted the Gregorian calendar in 1873, however, the extent of usage of the two systems varies.  The Japanese Patent Office, as an example, used the Imperial system up until 2000.

Within the Imperial calendar, one era ends and a new era starts with the accession of a new emperor.  The remainder of the corresponding Gregorian year then represents the first year of the new Imperial era.  Full subsequent Imperial years are then counted in synchrony with the Gregorian calendar, until the accession of a new emperor and the beginning of a new era.

To illustrate this, let’s look at the last three emperors of Japan in the figure below.



Wikipedia. (2019, May 25). “Akihito”. Retrieved May 26, 2019, from:

Wikipedia. (2019, May 26). “Hirohito”. Retrieved May 26, 2019, from:

Wikipedia. (2019, May 26). “Naruhito”. Retrieved May 26, 2019, from:


Emperor Hirohito came to the Chrysanthemum Throne on 25th December 1926, and his era was known as Showa.  When he died on 7th January 1989, Emperor Akihito acceded to the Chrysanthemum Throne, and the Heisei era began.  Emperor Akihito abdicated on 30th April 2019, and Emperor Naruhito acceded, thus beginning the Reiwa era.

1926 is the first year of the Showa era (S1), 1927 is the second Showa year (S2) etc.  1976 (Showa 51) is when the Patent Abstracts of Japan database began (containing bibliographic information of published unexamined patent applications).  The Showa era ended in 1989.  This year is Showa 64 up until the accession of the new emperor, when it becomes the first year of the Heisei era (H1).  Documents published in that year will have either a Showa 64 or Heisei 1 designation depending upon the exact date of publication.

Similarly, Heisei 2 is 1990 and so on through out the reign of Emperor Akihito.  The Japanese Patent Office (JPO) used the Imperial calendar up until 2000, when it then switched to using the Gregorian calendar for dates assigned to new patent publications.  Thus, the last documents published by the JPO using the Imperial calendar system were published in 1999 (Heisei 11).

The Heisei era ended on 30th April 2019 (Heisei 31) and the first year of the Reiwa era began the following day.


Types of Japanese Patent Documents

There are three main types of national Japanese patent documents.

The first are Kokai, or the publication of an unexamined patent application.  These are usually identified with a kind code “A”.

The second (relevant to patents prosecuted prior to 1996) are Kokoku, or the publication of an examined patent application.  These are typically identified with a kind code “B”.  After 1996, Japanese patent law changed and Kokoku documents were no longer published.

The third are Toroku, or the publication of a granted patent.  These are identified with a kind code “B”.


Retrieval of Japanese Patent Documents

When identifying, searching and retrieving Japanese patent documents, it is necessary to have an understanding of the numbering formats of the different document types discussed above.  The formats of each of three document types are illustrated in the following figure.


Toroku documents (on the right of the figure) are the simplest, having a two-letter country code “JP”, a seven-digit document number, and the kind code “B” suffix.

Kokai and Kokoku are a little more complex.

Kokoku documents (centre) have a two-letter country “JP”, a two-digit Imperial year code (corresponding to the Imperial era discussed above), followed by a six-digit document number, and the kind code “B” suffix.

Prior to 2000, Kokai documents (left of the figure) followed the same format as Kokoku documents, except that they have an “A” kind code.  From 2000 onwards, the two-digit Imperial year code was replaced with a four-digit Gregorian year – the other parts of the number format remained the same.

When working with Japanese patent documents, it is important to accurately identify the document concerned by careful consideration of the procedural stage and the year of publication, which may not be immediately obvious if one is not familiar with the various date formats described in this post.

Additionally, care should be taken to understand how specific databases require publication numbers to be entered.  If not, there is a risk of falsely assuming a document is not available in the database, when in fact it is, or worst, end up retrieving the wrong document.


Avoiding Pitfalls

Common pitfalls to avoid include determining whether or not the database you are using requires additional information such as an “S” or “H” within the publication number to distinguish the Showa and Heisei eras.  Some databases are indexed this way.

In such databases, JP54123456A would be searched as JPS54123456A, and JP10123456B would be searched as JPH10123456B.  Omitting this additional information can result in a document not being retrieved when it is actually available.

Further, documents from the early Heisei era can sometimes be presented with the leading zeros of the Imperial year omitted.  Thus, JP01123456 may come to you initially as JP1123456, which can easily be misinterpreted as a Toroku (granted) document rather than a Kokai (published application).

It is important to treat such documents carefully by first identifying the procedural stage you expect, and as necessary applying the right imperial year code to ensure the correct document is retrieved and worked with.

It is always advisable to double-check the documents you are working with by crossing-checking against other information such as application and priority data, document title, or other published family members.

Alistair Curson



European Patent Office. (2019, May 14). “Numbering system – Japan”. Retrieved May 26, 2019, from:

Japan Patent Office. “Searching for Patents, Utility Models, Designs, Trademarks”. Retrieved May 26, 2019, from:

Korteman J. (2019, April 01). “How to Read a Japanese Calendar”. Notes of Nomads. Retrieved May 03, 2019, from:

Reynolds I, Mori K. (2019, May 01). “Japan’s New Emperor Naruhito Ascends World’s Oldest Monarchy”. Bloomberg. Retrieved May 03, 2019, from:

Wikipedia. (2019, May 25). “Akihito”. Retrieved May 26, 2019, from:

Wikipedia. (2019, May 26). “Hirohito”. Retrieved May 26, 2019, from:

Wikipedia. (2019, May 26). “Naruhito”. Retrieved May 26, 2019, from:

World Intellectual Property Organisation: Handbook on Industrial Property Information and Documentation. (2005, December). “Presentation of Application Numbers”. Retrieved May 03, 2019, from:


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