Japan Standard Time or JST (日本標準時 or 中央標準時) is the standard timezone of Japan, and is 9 hours ahead of UTC. For example, when it is midnight (00:00) in UTC, it is 9 am (09:00) in Japan Standard Time. There is no daylight saving time, though its introduction has been debated several times. Japan Standard Time is the same as Korea Standard Time, Indonesian Eastern Standard Time and Yakutsk Time. During World War II, it was often called Tokyo Standard Time in Western contexts.
Before the Meiji era (1868–1912), each local region had its own timezone in which noon was set to when the sun is exactly at its zenith. As modern transportation like trains were adopted, this practice started to cause confusion. For example, there is a difference of about 5 degrees in terms of longitude between Tokyo and Osaka and because of this, a train that departed from Tokyo would arrive at Osaka 20 minutes ahead of the time in Tokyo. In 1886, Ordinance 51 was issued in response to this problem, which stated:
According to this, the was set 9 hours ahead of GMT (UTC had not been established yet). In the ordinance, the first clause mentions GMT, the second defines east longitude and west longitude and the third says the standard timezone would be in effect from 1888. Coincidentally, the city of Akashi in Hyōgo Prefecture is located exactly on 135 degrees east longitude and subsequently become known as Toki no machi (Town of Time).
With the annexation of Taiwan in 1895, Ordinance 167 was issued to rename the previous Standard Time to and establish new at 120° longitude. Western Standard Time, which was used in Taiwan and some parts of Okinawa, was abolished by ordinance 529 in 1937. Territories occupied by Japan during World War II, including Singapore and Malaya, adopted Japan Standard Time for the duration of their occupation, but reverted after Japan's surrender.
In 1948–1951 occupied Japan observed daylight saving time (DST) from the first Sunday in May at 02:00 to the second Saturday in September at 02:00, except that the 1949 spring-forward transition was the first Sunday in April. More recently there have been efforts to bring back DST in Japan, but so far this has not happened.