Flag ratio: 2:3

The national flag of Japan, known as the Nisshōki (日章旗) or Hinomaru (日の丸 "sun disc") in Japanese, is a base white flag with a large red disc (representing the sun) in the centre. A legend says that its origins lie in the days of Mongol invasions of Japan in the 13th century, when the Buddhist priest Nichiren was supposed to have offered the sun disc flag to the Emperor of Japan, who was considered a descendant of the sun goddess Amaterasu. In fact the sun disc symbol is known to have been displayed on folding fans carried in the 12th century by samurai involved in the feud between the Taira and Minamoto clans. It was widely used on military banners in the Sengoku ("Warring States") period of the 15th and 16th centuries. Subsequent Shogunates established it as the flag to be flown from Japanese ships.

By the time of the Meiji Restoration of 1868, it came to be regarded as the national flag. Though the sun disc design was officially adopted for use in naval flags in 1870, it was not formally adopted as the national flag until August 13, 1999 by a decree that also confirmed its exact dimensions: the flag has a vertical-to-horizontal ratio of 2:3 with the disc, the diameter of which is three-fifths of the flag's vertical height, at the exact center. A well known variant is the sun disc with 16 red rays which was historically the flag for use in Japan's military, in particular the navy until the end of World War II. It is now used again as Japan's naval ensign.

In Western heraldry, it could be blazoned Argent, a torteau or Argent, a roundel gules.

In 1999, the establishment of Law Concerning the National Flag and Anthem officially designated Hinomaru as a national flag of Japan.