The rapid progress in low birthrate and aging in Japan has brought a large increase in the cost of social security. This study seeks to predict the trajectory of Japaneses social policy by taking population problem, technology and labor in the form of change, legacies of previous welfare structures, and value change into account. First of all, medical spending will increase considerably while the growth of the pension spending would be moderate by 2030 due to the achievements of past reforms. Second, while the importance of social insurance contribution in terms of financial components will be maintained, tax-based expenditure will rise sharply. In addition, social investment in the family and the labor market increases. However, considering the strength of political influence of elderly, conservative discourse of reform of the ruling power, and the slow pace of the changing social values, the turn of the welfare state will be based on functional responses in Japan.