This study analyses the formation of a policy system that reduced income inequality in Japan in the 1960s, a period of rapid economic growth. According to comparative research, the Japanese state is an example of small government with income equality. Japan’s income inequality rose in the 1950s, and at that point, the government faced a decision about how to reduce income inequality, and particularly whether to expand social security and government size. This study uses primary materials to analyse how and why Japan became more egalitarian while maintaining a small-government state, focusing on fiscal rules set by the Ministry of Finance, which adopted a balanced budget rule that prevented the issuance of public bonds and limited the tax burden ratio. As reflected in the government’s Income Doubling Plan, this development led to a trade-off among factors, such as social security, public works, and tax cuts, which led to the subordination of social security. Despite public debt issuance in 1965, which was contrary to two fiscal rules, social security did not expand because of fiscal rigidification. Throughout the 1960s, spending on public works and income tax cuts was prioritised over social security, resulting in small government but also income equality.