Since the end of 70's, a theory of physical education which emphasizes fun, so called "Tanoshii Taiiku", has been generalizing in Japan. But recently it is said that "Tanoshii Taiiku" ended in the failure. The purpose of this paper is to search the cause of this failure. That is because we don't want that the same failure is not repeated in the future. In this study, we searched the cause of the failure from following two aspects. 1) the aspect which is the trap hidden in the theory of "child-centered education". 2) the aspect of the relation between theory and practice.