This article deals with the relation between the medical discourse and that in the transgender community in Japan, which encompasses many participants of diverse gender identities. The participants communicate with one another not only in person but also by various means including internet. Sex-change surgery was recently legalized for those whose agony concerning gender identity cannot be removed by other means. A certain type of gender identity problems was medicalized as 'gender identity disorder'. Since the mass media reported a person who had undergone sex change surgery in Saitama Medical College, 'gender identity disorder' was socially acknowledged. Several affirmative reports contributed to make 'gender identity disorder' socially accepted. It seems that the medicalization is a great relief for those who have full assurance that only sex-change surgery can resolve their gender identity problems. This type of transgender people is categorized as TS (trans-sexual) in the transgender community, which also differentiates two other categories, TG (trans-gender), who may not undergo the surgery but take hormone treatment and TV (transvestite), who only manipulate their closes. Bu referring to the medicalization, a type of discourse that legitimizes and centers TS occurred in the community. It insists that only TS is pure and true and TG is less pure and further TV is rather false. While the medicalization aimed at saving transgender people, it leaded to the center-peripheral structure and to peripheralized participants' agony in the community. This article clarifies the process and logics how this discriminative structure arose, by looking at the medical and community discourse.