The topic of this paper is to analyze the sequence of events and circumstances of the social security system in post-war Japan from the perspective of income distribution. The amount and quality of benefits has been increased in social security in Japan. However, with the reforms in 1973, the expansion of benefits was implemented without increasing the burden of costs. Under the current integrated reform of social security and tax, the expansion of benefits is controlled while a regressive consumption tax is used as a source of revenue. It is thought this is leading to a decline in the function of income distribution.