Nationals of many countries are eligible to enter Japan without a visa unless the purpose of the visit is to reside in Japan, to obtain employment or to otherwise engage in remunerative activities.
The following is a list of nationals of countries that have "Reciprocal Visa Exemption Arrangements" with Japan:

For a period of 6 months or less

Austria, Germany, Ireland, Liechtenstein, Mexico, Switzerland and the United Kingdom (UK citizens only)

For a period of 3 months or less

Argentina, Bahamas, Belgium, Canada, Chile, Costa Rica, Croatia, Cyprus, Denmark, Dominican Rep., El Salvador, Finland, France, Greece, Guatemala, Honduras, Iceland, Israel, Italy, Lesotho, Luxembourg, Macedonia, Malta, Mauritius, the Netherlands, Norway, Portugal (except when the passport was originally issued in present or former Portuguese colonies), San Marino, Singapore, Slovenia, Spain, Surinam, Sweden, Tunisia, Turkey and Uruguay

For a period of 90 days or less

Andorra, Australia, Barbados, Czech Rep., Estonia, Hong Kong, Hungary, Latvia, Lithuania, Monaco, New Zealand, Poland and the U.S.A.

For a period of up to 14 days

Brunei

Nationals of countries that do not have "Reciprocal Visa Exemption Arrangements" with Japan must obtain a visa.

A "Temporary Visitor's Visa" is usually required as permission to stay in Japan for a period of up to 90 days for non-remunerative activities such as sightseeing, participating in amateur sports, visiting relatives, taking inspection tours, participating in lectures or research, attending conferences, making business contacts or other similar activities.

Needless to say, the "Temporary Visitor's Visa" cannot be used for any remunerative purposes, which involve profit making or payment acceptance within Japan by the visitor.

To apply for a visa, the applicant must apply in person to a Japanese Embassy or a consulate, usually in his or her home country. The following documents must be submitted whatever the purpose of visit you are going to make:

(1) Valid passport;
(2) Two passport photos taken within the six months previous to the date of application;
(3) Two official visa application forms, available at the embassy or consulate;
(4) Documents certifying the purpose of the visit.

As the type of documents required for the application may differ according to the purpose of your visit, the applicant is advised to check with the Japanese Embassy or consulate beforehand.

Visa Fee Exemption: The nationals of some 60 countries around the world are exempted from visa fees.

The Ministry of Foreign Affairs of Japan Home Page

http://www.mofa.go.jp     
JNTO Website > Guide to Japan