Recently, there are many articles with which SDPJ is dealt. The aim of this article is to investigate the formation process of the proposition “kouzou-kaikaku” (the reform plan of SDPJ) and to verify how the plan had held place in SDPJ at that moment. Especially I will focus on the rising and fall of the faction “Eda-Ha” which was represented by Eda Saburou (one of the influential reformers in SDPJ). It would have intended to reform SDPJ in large measure in 1960's. But in spite of its passion, the reform faced the various oppositions by the major (left) factions within SDPJ. As the consequence, Eda-Ha failed to reform SDPJ. We can see many reasons why the theory “kouzou-kaikaku” has lost its position in SDPJ. Up to this time, it is said that the decline of Eda-Ha with the intention of the reform caused to the decline of SDPJ. I present other reason of the decline from the alternative points of view. By doing so, I intend to contribute further development of the studies on SDPJ.