The purpose of this study is to clarify the characteristic types of professional ideology which began to arise among the various parties concerned with baseball in the Taisho period, by using a historico-sociological perspective. The objects of this study are three teams, i.e., the Japan Athletic Association (in Japanese, Nippon Undo Kyokai), the Tenkatsu baseball team (Tenkatsu Yakyu Dan) and the Daimai baseball team (Daimai Yakyu Dan) because it would be conceivable that these three teams can be organized in a manner based on the characteristic type of professional ideology. The perspectives and frameworks for analysis are made up concretely by ideologically interrelated types between the baseball system and the economic system from the viewpoint of that system. That is, as two model types regarding the formation of ideology, it was thought that there was one type of autonomous formation (Type A) which takes precedence over the profit within the baseball system, and the other (Type B) of a heteronomous formation which favours the profit within the economic system in disregard of that of the baseball system. As a result of analyzing the above three teams, the arising of a professional ideology can be classified as fdllows: 1) The Japan Athletic Association was a party which looked forward to internal reform by natural growth, and promoted professionalism in order to realize a particular ideal, that is to develop sound baseball within their system without allowing the involvement of an economic order, i.e., enterprise. (Type A) 2) The Tenkatsu baseball team was an "enterprise-led" type of party, which looked forward to an external reform of the system with the desire to promote professionalism by allowing the involvement of the economic order and being utilized by such an order. (Type B) 3) The Daimai baseball team possessed the same ideology as type B, but it was an "enterprise-leading" type of the baseball system, a new concervative party which tried to maintain an amateur qualification. (Type C) These three types of professional ideology at the dawn of the baseball period are not only paid attention to from the viewpoint of the effect on the establishment of the later professional baseball system, but also need to be examined further in order to resolve the fundamental problems regarding the professionalization of the present world of sport considered in its entirety.