The outlets in Japan are Type A and are identical to North American two-prong outlets where each slot is the same size. Common phone chargers will work without any problem.
However, if your plug has three prongs—or two prongs of different sizes—you’ll need to buy an adapter. Simple ones can be found online for under $5. You may also want to purchase a universal adapter such as this one that can be used in almost any country.
The voltage in Japan is a bit less than ours, so all our usual household items work fine as long as you have the plug adapter. Read this article if you want more details.
