The national flag of Japan is a white rectangular flag with a large red disk (representing the sun) in the center.
The Japanese flag is officially called Nisshōki (日章旗, “sun-mark flag”) in Japanese, but is more commonly known as Hinomaru (日の丸, “circle of the sun”).
The Nisshōki flag is designated as the national flag in Law Regarding the National Flag and National Anthem, which was promulgated and became effective on August 13, 1999. Although no earlier legislation had specified a national flag, the sun-disc flag had already become thede facto national flag of Japan. Two proclamations issued in 1870 by the Daijō-kan, the governmental body of the early Meiji Era, each had a provision for a design of the national flag. A sun-disc flag was adopted as the national flag for merchant ships under Proclamation No. 57 of Meiji 3 (issued on February 27, 1870), and as the national flag used by the Navy under Proclamation No. 651 of Meiji 3 (issued on October 27, 1870). Use of the Hinomaru was severely restricted during the early years of the American occupation after World War II, although restrictions were later relaxed. Wikipedia