A light source device (411) has a lamp body (411A) including a light source lamp, a reflector (417) and an anti-explosion glass (418), and a lamp housing (411B) for accommodating the lamp body (411A). A plurality of projections (411B8) protruding along an optical axis of a light beam irradiated by the light source lamp are formed on the lamp housing (411B). Further, the reflector (417) has an approximately concave cross section and a positioning surface (417C) that touches the projections (411B8) of the lamp housing (411B) to locate the lamp body (411A) relative to the lamp housing (411B) is provided on a distal side of the concave section. The positioning surface (417C) is continuously flush.