In the present study, an attempt was made to clarify the whole structure and originality of Taiiku-gaku (Science of PE, Health and Sport Sciences), centering on the ‘tree of sciences’ theory of René Descartes (1596-1650). In the study of physical education philosophy, some attempts have been made to reveal the whole structure and originality of Taiiku-gaku. It seems more appropriate to discuss and address this issue by defining certain principles at the outset. For this purpose, it would informative to examine this issue from the philosophical perspective of Descartes' ‘tree of sciences’ philosophy. In the history of discussion to clarify the whole structure and originality of Taiiku-gaku among researchers, three essential characteristics become evident: (1) Science should be aimed at being practical and useful, (2) it should contribute to our well-being, and (3) it should aid the search for wisdom. Up to now, it appears that Taiiku-gaku as a science has advanced in line with these characteristics. However, Descartes revealed his vision of the purpose of science through the “tree of sciences” in his Principia Philosophiae (Principles of Philosophy). He analogized the whole structure of science (philosophy) to a tree with its roots, trunk, branches and fruit. The present paper therefore utilizes this concept of Descartes to answer the question. In conclusion, the whole structure of Taiiku-gaku could be understood as being analogous to a tree, and the originality of Taiiku-gaku does not depend on humans themselves or human movement as a fundamental research object. The originality of Taiiku-gaku can be analogized with the achievement of Generosity, which is the goal of the “tree of sciences”. Thus, on the basis of output diversity analogous to fruit taken from branches of the tree, the originality can be characterized as a science that tries to achieve the highest performance of human movement imaginable. More enlightened discussion can ensue by reconsidering the concept of taiiku (which is different from Physical Education) and the identity of Taiiku-gaku researchers.