The voltage used in Japan is 100 V AC, which is different from many other regions in the world. Some devices may be damaged if they are designed for another region. For example, you may need an adapter for your computer if you are bringing it from the United States (120 V) or Europe (220-230 V). Some appliances, however, such as Apple iPhone chargers, are designed to adapt automatically to different voltages. Please check with the manufacturer of your electrical product before plugging it into a Japanese socket.
Despite Japanese outlets looking identical to North American outlets, it is wise to purchase an adaptor if bringing North American appliances to Japan, as some outlet configurations will not fit into Japanese sockets.
The frequency of the electrical current is 60 Hz in western Japan (Osaka, Kyoto, Hiroshima, Nagoya, Shikoku, and Kyushu) and 50 Hz in eastern Japan (Tokyo, Yokohama, Tohoku, and Hokkaido). Most appliances are not affected by this slight difference.
Three-pronged plugs are not used in Japan, so you will have to buy an adapter. You can buy different kinds of adaptors to suit your needs at most appliance stores either before your visit or after arriving in Japan.