We discuss the concept of social capital, which has received much attention recently. Social capital is important for the following 2 key reasons: (1) a highly democratic polity and a strong economic performance that attaches great importance to the public good can be achieved on the basis of high social capital; and (2) social capital can effect health status in the human population, and widening of income inequality harms human health through the erosion of social capital. In addition, there are 3 political implications of social capital for Japanese society: (1) social capital has implications for the political decision of whether Japanese society should adopt a "medium burden for medium welfare" or a "low burden for small welfare" model together with the concept of social overhead capital; (2) reciprocity, which is one of the primary components of social capital, is similar to the philosophy underlying the health care system of Japan; (3) Japanese society needs to change from a society that emphasizes the relationships between its members to a society that is open to outsiders and has sufficient opportunities.