Emperor's Birthday (Japanese: 天皇誕生日, Hepburn: Tennō tanjōbi) is an annual public holiday in Japan celebrating the birthday of the reigning emperor, which is currently 23 February as Emperor Naruhito was born on that day in 1960. It is enforced by the Emperor Abdication Law passed in 2017.

The name of Tenchosetsu (天長節) is ancient, and derived from the birthday of Emperor Xuanzong of Tang. It was changed to "Chiaki-bushi" (千秋節) in 729 in the first year of Tenpyō, but it was renamed to "Tencho-setsu" (天長節) in the 7th year of Tenpyo (748 in the first year of Katsuho) 19 years later. "Tencho" (天長) is taken from Laozi's "Tencho Chikyu" (天長地久).

The earliest historical record of an Emperor's birthday celebrations relates to the 6th year of Hōki in Emperor Kōnin's reign (775 CE). The Emperor's birthday was already celebrated during the Heian period. This is recorded in the record of Hōki 10 (779). It is recorded that:

This day being the Tencho, a great drinking feast was held for all the ministers, fine sake that are favoured [by the Emperor] were presented. After the feast, stipends were awarded. (Old Japanese: 是日天長大酺群臣献翫好酒食宴畢賜禄有差)

An edict dated the 11th day of the Ninth month is also recorded:

The 13th day of the Tenth birthday being Our birthday, each year on this day, it is both emotional and celebratory. On this day, all the monks and nuns of the monasteries must on this day turn the sutras and perform the rituals, and no animals should be butchered throughout the country, and all of the officials of inner and outer courts are awarded feasts for the day. The day will be called Tenchosetsu. Thus the moral merit is used to repay the deceased imperial mother, and the celebration is spread throughout the land. (十月十三日是朕生日毎至此辰威慶兼集宜令諸寺僧尼毎年是日転経行道海内諸国竝宜断屠内外百官賜酺宴一日仍名此日為天長節庶使廻斯功徳虔奉先慈以此慶情普被天下)

There is also a description in the "Oyudono Diary" (お湯殿の上の日記) as a record of the Muromachi period.

On 26 August 1868 (11 October 1868), a decree by the Daijo-kan said, "22 September, the Emperor's Birthday is equivalent to the Emperor's Birthday." On 22 September (6 November 1868), the Emperor's Birthday was celebrated as a national holiday. In the 2nd year of the Meiji era (1869), the ministers of each country were invited to the Enryokan to receive a drink, and in the 3rd year of the Meiji era (1870), various officials, non-employees, Kazoku, etc. worshiped. The ministers and below received a feast at each ministry, and royal gun salute was shot on various warships. The ritual of the Emperor's Festival was completed in 1872, in the same year of the Emperor's Birthday.