This study aims to explore the aspects of professional capital accumulation of elementary school teachers in the developmental period according to their experience in special graduate training, which is an effective way to overcome the problems of current education. In order to achieve the purpose of the study, interviews were conducted with 8 elementary school teachers in the second year of special training in the graduate school of K University. As a result of the study, the professional capital of elementary school teachers in the developmental period before the special training of the graduate school is as follows. First, it was found that as human capital the ability to help students and to actively search to utilize various teaching and learning were enough, but to help colleagues was insufficient. Second, as social capital, the level of cooperation was achieved in the limited cooperative network centered on the same grade. Third, as a decision-making capital, judgment as a teacher was prioritized over the curriculum, but the experience of reflection was insufficient. The changes in professional capital experienced through the special graduate school training course are as follows. First, as human capital, they realized how to broaden their perspective through theoretical search and enhance expertise through research. Second, it was recognized that the intensity of cooperation had increased, and the social network had expanded. Third, as a decision-making capital, the ability to make autonomous judgments was insufficient as a researcher, but the formation of practical knowledge was confirmed through sufficient reflection experience on education. The discussion point centered on the results of this study is, first, that special graduate training can greatly help elementary school teachers in their developmental period to accumulate social capital. Second, the special graduate training course can be a way to cope with the ‘geromorphism’ as a teacher, which is a characteristic of teachers' life development.