The changes in income inequality during the post-war period in Japan are investigated quantitatively and extensively in order to shed some light on the relationship between income inequality and the rapid economic development experienced in Japan. Following a presentation of some summary pictures on income inequality in the Japanese society the following issues are discussed: the institutional aspect of distribution of wage earnings, educational impact on employment income inequality, and other educational aspects. As concluding remarks, some empirical observations on income inequality including assets-related income are presented. An examination of the data leads to the tentative conclusions that the employment income inequality in the post-war Japan may have been to some extent improved in accordance with Japan's rapid economic development, while the income inequality in a broader sense may have become worse, especially due to the recently experienced inflation. The emergence of rising trends of consumers and wholesale prices has become clear since the end of the 1960's. Under these circumstances, the new element which would generate social troubles in income distribution is added to Japan's society. These new elements may not be overcome by a further economic development, but some significant changes in institutional set-up may be needed such as the changes in the private ownership. (Author/AM)