After the revision of the course of study in 1977, "Happy physical education" theory has been reflected in the physical of elementary school. On the other hand, there is a report that many of children in Japan "escape from learning". In this study, I place joy and pleasure the students tastes when they can understand what they cannot understand, or they can do what they cannot do as "the pleasure of change". And I try to explain especially the existence of "the pleasure of change" in the learning process in the class of horizontal bar exercise.