Japanese power outlets have two prongs, just like the U.S. two-pronged outlets. Two-pronged devices will work in either country, but three-pronged U.S. plugs will not work in Japanese outlets without an adapter.
U.S. plugs and outlets are polarized, with one plug slightly larger than the other, meaning they will allow Japanese un-polarized or U.S. polarized plugs. Japanese outlets are usually polarized but sometimes not, meaning sometimes U.S. plugs will not fit.
Outlet voltage in the United States is 110 volt, while in Japan it is 100 volt.
Outlet frequency in the United States and west Japan is 60 Hertz, while in east Japan it is 50 hertz. If near the 50/60 divide, travelers can check with a local electric shop, as frequency can change between cities.
The voltage and frequency of a device is usually found engraved on the device, the AC adapter or on a sticker affixed to the device. Some devices have voltage and frequency ranges, such as laptops, which are frequently 100V-240V and 50-60Hz, allowing them to be used many places in the world.
Most devices will not be adversely affected by slight differences in voltage, but travelers should check more sensitive devices such as microwaves or computers, as the consequences of connecting directly to an improper voltage or frequency can be more dire. To change voltage, travelers can use a converter or step-up or step-down transformer, though frequency changes can be more difficult and expensive to deal with.
