The national flag of Japan is a white flag with a large red disc (representing the Sun) in the center. The flag's official name in Japanese is NisshÅki "sun flag" but the flag is more commonly known as Hinomaru "sun circle". The Hinomaru was widely used on military banners in the Sengoku period of the 15th and 16th centuries. However, the flag was not adopted nationally until August 13, 1999, by the Law Concerning the National Flag and Anthem.
source: wikipedia