This paper reassesses the history of psychiatry in Japan through application of the theory of disciplinary power by Michel Foucault. The society of the early Meiji era (1868-1912) is defined as a disciplinary society within the scope of discourses on punishment and general social reforms. By focussing on a close reading of both canonical and marginalised fragments of psychiatric texts, this analysis reveals their constitutive character for the establishment of psychiatric discourses. These texts, rooted in biological psychiatry, are shown to stress the hazard that mental illness presented to the nation. Recourse to juridical problems, which derive from enacting a European model of law, provides an explanation for the necessity of psychiatry as a social institution. The key point is to identify a discursive break between two major legal acts dealing with the confinement of the mentally ill: the Mental Patients Custody Act of 1900 and the Mental Hospital Act of 1919. The first deals mainly with administrative issues, while the latter was formed under the influence of an emerging psychiatric power. The Mental Hospital Act refines the disciplinary network operating in the social space, while blurring the discursive fissure between traditional care and psychiatric techniques.