Electrical outlets in Japan are for the most part consistent with North American sockets. While the voltage in Japan in 100 Volt, lower than that of North American plugs at 110 Volt and central Europe and surrounding countries at 230 Volt, for the most part, they are compatible and work just fine.
Plugs in Japan come in several varieties but are most often non-polarized with two pins. Additionally, plugs can also be grounded with three or two pins.
Some electronics from North America will work in Japan without the use of an adapter, however, for some electronics, it is recommended to use one. Hairdryers, curling irons, and straightening irons and other heated devices tend to overheat or not work properly unless used in conjunction with an adapter in the electrical outlets in Japan. Additionally, many hotels offer special equipment such as blowdryers that are specifically adapted for visitors to use.
For those traveling outside of major cities like Tokyo, Kyoto, and Osaka, an adapter may be useful. Additionally, for some electronic heated devices, an adapter is recommended when traveling in Japan.