In which year did the current national flag of Japan became official?

The national flag of Japan is a rectangular white banner bearing a crimson-red disc at its center. This flag is officially called Nisshōki (the "sun-rise flag"), but is more commonly known in Japan as Hinomaru (the "circle of the sun"). It embodies the country's sobriquet: Land of the Rising Sun.

The Nisshōki flag is designated as the national flag in the 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 the de facto national flag of Japan. Two proclamations issued in 1870 by the Daijō-kan, the governmental body of the early Meiji period, 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 Allied occupation of Japan after World War II; these restrictions were later relaxed.