The electricity supply throughout Japan is 100 Volts AC, 50Hz in eastern Japan including Tokyo, 60Hz in western Japan including Nagoya, Kyoto and Osaka.
Because of the difference in voltage, if you take an appliance from the UK make sure it is a dual-voltage one, or take a transformer.
The electric sockets are the type with two flat pins.
An international adaptor is therefore essential. They are available in Japan, but buying one before you travel might save time.