The voltage in Japan is 100 Volt, which is different from North America (110V), Central Europe (220V) and most other regions of the world.
Japanese electrical plugs have two, non-polarized pins, as shown above. They fit into North American outlets.
Japanese power outlets are identical to ungrounded (2-pin) North American outlets. While most Japanese outlets these days are polarized (one slot is slightly wider than the other), it is possible to encounter non-polarized outlets in some places.

Some North American equipment will work fine in Japan without adapter and vice versa, however, some sensitive equipment may not work properly or even get damaged.
If you intend to purchase electronic appliances in Japan for use outside of Japan, you are advised to look for equipment specifically made for oversea tourists.

The frequency of electric current is 50 Hertz in Eastern Japan (including Tokyo, Yokohama) and 60 Hertz in Western Japan (including Fukui, Nagoya,Kyoto, Osaka), however this frequency difference affects only sensitive equipment.

Some of laptops /notebook PC have transform system in AC adaptor by itselves.