In Japan, a developed country in Asia, the Land Improvement Act systems have worked as a measure of social capital accumulation as well as an adjective law in implementing irrigation projects since 1949. This paper illustrates the status and problems in applying the concept of social capital to agricultural and rural development policy systems in developing countries, EU and Japan. The results obtained are summarized as follows: (1) it is desirable that governments formulate public policies that are appropriate for correcting inefficiencies in resource distribution for accumulating social capital, so that the governments play a significant role in developing and supporting social capital; (2) the effect of policies in the areas, where government-supported land improvement projects have been implemented, has been improved, subsequent to which the efficient use of the national budget allocated for the projects has been improved, while the projects significantly contribute to the national land conservation and social stability by continuously promoting minimum social capital accumulation nationwide. In addition, Japan and countries in the Asian monsoon region, which hold the five elements in common that constitute the characteristics of rice field irrigation in humid climates, should take over the advantages of the land improvement project system while learning from the success achieved by the LEADER+ programme in Europe, where society precedes Asian countries concerning the problems of decline in the birth rate, and expansion of an aging society.