Everyone traveling to Japan for a visit, to work or to immigrate requires a passport issued by their own country unless you are traveling on military orders. If you are only visiting Japan, you may or may not need a visa. Many countries, including the United States, the United Kingdom, Germany and Canada, have reciprocal agreements with Japan and citizens of these countries can enter Japan for the purpose sightseeing, visiting relatives or attending business meetings without a visa. These people can usually stay up to 90 days per trip. But a word of caution, if you are in Japan without a visa, you can not work while you are here. If your country does not have this type of agreement with Japan, you do require a visa so it is best to check with the Japanese Embassy or Consulate in your country to be sure.
Military personnel on orders can enter using their Military ID card and orders. Family members require a passport but do not need a visa.
Those who are in Japan only to visit can not take advantage of the re-entry permit. However, all aliens who are in the country on a semi-permanent or permanent basis must complete a re-entry form prior to leaving Japan if they wish to return without getting another visa and starting this process all over again. There are two types: single entry and multiple entry permits and there is a fee for each. Currently, that fee is 3000 Yen for a single entry and ¥6000 for a multiple entry permit. Perhaps the most convenient place in Tokyo to acquire this permit is a the Tokyo City Air Terminal (TCAT). Otherwise, the nearest office of the Japan Immigration Service can take care of this for you.
I'm sure you will find that the immigration laws for visitors are not much different than most
modern countries. This page is not intended to give you everything you need to know. If in doubt, you should always contact the professionals at the embassy or consulate before you travel.