In our project, which is called the "Pocket Money Project," researchers from the four East Asian counties, Japan, Korea, China, and Vietnam, jointly conducted research in various combinations on the relationship between money and children in each country. In this paper, we outline the results of the project. First, we summarize the three main findings: life in consumer society, the structure of parentchild relationships, and that of peer relationships for children in these four countries. Second, we propose the theoretical framework of our "cultural psychology of differences," which we call an "expanded mediational structure (EMS)," based on the results. The "cultural psychology of differences" aims not to extract crystallized culture as a substance but to show the possibility of understanding a different culture with a prescription to handle and analyze the process in which it is being crystallized, and through this, ultimately to show a way of practice to understand different cultures.