Jinmu Tenno Sokui Kigen (Imperial era) (神武天皇即位紀元)

Jinmu Tenno Sokui Kigen (Imperial era) is a Japanese way of counting years, the first year being that of accession of Emperor Jinmu, the first emperor, to the throne.

At present, the western calendar system is employed (based on Japan standard time).

It is commonly called Koki (Imperial era) and is also referred to as Koreki (Imperial calendar), Jinmureki (Jinmu calendar), Jinmukigen (Jinmu era), Nikki (Japan era), etc. It was also abbreviated simply as Kigen (Era). In alphabetical notation of the number of years, Koki is used in the same way as Heisei (the Japanese era since the enthronement of the present Emperor) and Imperial era 2600 is written as Koki 2600, etc.

The year by Jinmu Tenno Sokui Kigen becomes larger than the Western calendar system (the Gregorian calendar) by 660 years. This difference does not change from year to year and is constant. For example, the year 2000 by the Western calendar system corresponds to the year 2660 by the Jinmu Tenno Sokui Kigen (Koki).

From the Meiji period to the end of the world war II in 1945, Jinmu Tenno Sokui Kigen was often used together with gengo (an era name). Nowadays, Jinmu Tenno Sokui Kigen is rarely seen in public calendars but it has not been abolished officially. Even now, Jinmu Tenno Sokui Kigen is legally used together with gengo and the Gregorian calendar and, for example, the style of placing intercalary years is determined based not on the Gregorian calendar but on Jinmu Tenno Sokui Kigen (Imperial Edict No. 90 issued on May 10, 1898). In addition, it is used by a small proportion of amateur devotees of the conservative history of Japan and Japanese literature, persons concerned with Shinto religion (State Shinto), All Japan Iai Do Federation, etc.

In "The World Factbook" in the Web page of Central Intelligence Agency, the Imperial era of Japan is described as "Independence 660 BC (traditional founding by Emperor JIMMU).

However, it is not thought to be a fact that Emperor Jinmu acceded to the throne in 660 B.C. by the Western calendar system because the presence of Emperor Jinmu is difficult to prove and establishment of the Yamato sovereignty (the ancient Japan sovereignty) is archeologically believed to be in around the 2nd century A.D. based on the age of appearance of kofun (tumuli). Archeologically, this period corresponds to the early Yayoi period but, in old times, it was believed to be the last stage of the Jomon period.

In addition, along with the memorial events of Kigen 2600 held from 1938, excavation and research of the outer garden of Kashihara-Jingu Shrine was carried out under supervision of Masao SUENAGA to find remains of large settlements of the end to last stage of Jomon period and a big oak tree buried standing with its roots spreading to a width of 16 square meters. According to the writing of Keiyo KANUMA (emeritus professor of Tokyo Gakugei University), this was all brought into Michigan University of the US and subjected to the radioactive carbon dating, to be found that this was a tree of 2600 years back from then with an error of ±200 years. Based on this fact, there is a theory that the legends of Emperor Jinmu described in "A Record of Ancient Matters" and "Chronicles of Japan" reflect some historical fact.


It was instituted on December 15, 1872 by Dajokan Fukoku (Decrees of the Cabinet) No. 342 and was executed on January 1, 1873, at the same time with employment of the solar calendar in Japan.

Ceremony on November 25 on the occasion of employment of the solar calendar and institution of the Imperial era with accession of Emperor Jinmu to the throne as the starting point (Dajokan Fukoku No. 342, 1872). To publicly notify the recent decisions to employ solar calendar and institute the Imperial era with accession of Emperor Jinmu to the throne as the starting point, a ceremony will be held on the coming 25th day. However, those in mourning should refrain from coming to the court.

Reason Why Year of Accession of Emperor Jinmu was Decided to be 660 B.C.

The Oriental zodiac repeats itself every 60 years and the years can be calculated easily. Thus, by going back from the chronology written in Chronicles of Japan, the year when Emperor Jinmu acceded to the throne comes to correspond to 660 B.C..

In the Meiji Period, Michiyo NAKA, a historian, put forward a theory that, in establishing a way to count years, Chronicles of Japan employed the Shinisetsu which was popular in Former Han to Later Han (dynasties of China) and counting back 1260 years from the year 601 when Empress Suiko set the capital in Ikaruga, the year 660 B.C was decided to be the year of, a great revolution, the enthronement of Emperor Jinmu. This is related to the note by Jo Gen in "Yi wei", the surviving fragment of a book on Shinisetsu (isho) which was banned by Emperor Yodai of Sui and got scattered and lost, where 60 years, one cycle of the Oriental zodiac, were defined as 1 gen and 21gen as 1 bou, and it was suggested that, in a specified zodiac year every 1260 years (= 60 ' 21) thus calculated, a national-scale revolution (change of dynasty) would be carried out.

On the first day of the month, the Emperor acceded to the throne at Kashiwara no Miya Shrine. This year was decided as the starting year of the Emperor.
('On February 11, 660 B.C., the Emperor acceded to the throne at Kashiwara no Miya Shrine and this year was made the first year of the Emperor'; "Chronicles of Japan," Paragraph on February 11, the first year of Emperor Jinmu.)

Imperial Era 2600 During Wartime

Incidentally, the "Type zero carrier fighter" of the Imperial Japanese Navy, well-known as the Zero fighter, is a name connected with the fact that it was employed in the year 2600 in the Imperial era (1940 in the Gregorian calendar [numbers in the type name of the weapons were based on the last two digits of the Imperial era]). In the case of the Imperial Japanese Army, the number for the weapons employed in the same year was not zero as in the Navy but 100 such as Type 100 heavy bomber, Type 100 headquarters reconnaissance plane, Type 100 transport plane, etc.

In 1941, the fighter employed by the Army was named as Type 1 fighter (commonly called as Hayabusa (falcon)).

Imperial Era and Yasuda Mutual Life Insurance Co.

In 1970's, Yasuda Mutual Life Insurance Co. (now Meiji Yasuda Life Insurance Co.) decided to build a personal information management system. At that time, the man in charge of the system was anticipating the Year 2000 problem, which might happen 20 some years later. Therefore, as the last two digits of the year count, he decided to employ not that of the Gregorian calendar or the era but that of the Jinmu calendar (Gregorian calendar - 40). By doing so, Yasuda Mutual Life Insurance Co. postponed the Year 2000 problem for 40 years.

Similar Eras

In addition to Japanese 'Imperial Era,' there are cases where original eras different from the Western calendar system or Islamic calendar were established or old eras were converted to the Western calendar system for use. The following are such examples. However, they were used for short periods of time and many of them are not in use now.

Genghis Khan Era (Genghis Khan Era. Royal Territory of Eastern Mongolia, Mongolian United Autonomous Government).

Turkish Era (Turkish era. Republic of Turkey. The first year is the enthronement of the first Turk Khan on Mongolian plateau).

Iranian calendar (also referred to as Cyrus era. Iran. This existed from a long time ago but was officially employed in the Pahlavi dynasty).

Era starting from the death of Buddha (Kingdom of Thailand. This has been present in Southeast Asia for a long time and is still in use).

Yellow Emperor era (China)
Dangun era (Republic of Korea)
This was given a legal basis on September 25, 1948 but, with establishment of an act to abolish the system of Era in 1961, its use is prohibited on a public occasion since January 1, 1962.

Ethiopian calendar

[Original Japanese]