United States → Japan
United States plugs
Type A
Type BJapan plugs
Type AType BShared plug types: A, B
Compatibility: Compatible
Voltage — United States 120V — Japan 100V
Voltage difference is small. Most electronics will work safely.
Device compatibility (phones)
Phones almost always support 100–240V, so yours should work safely. Check your charger label to confirm.
You likely only need a plug adapter (if socket shapes differ). Voltage is close between these countries.