In Japan, sector voltage is 100V and frequency is 50-60hz (50hz in Eastern Japan, 60hz in Western Japan). So before leaving your country, check your electric items that you plan to use in Japan.

Electrical outlet used

Type A JIS 8303 class 2 (without ground)

Type B JIS 8303 class 1 (with ground)

Type A is more commonly used.
You can buy transformers and electrical outlet adapters in specialized stores in your home country or even at some stores in international airports.
If you have many electrical appliances, it is recommended to bring a multi-outlet from your own country.