A light source device includes: a base member; a semiconductor laser mounted on an upper surface of the base member; a lateral wall portion having: a lower surface facing the upper surface of the base member and being a non-reflecting surface, and a reflecting surface that reflects light emitted from the semiconductor laser, is connected to the lower surface of the lateral wall portion at a lower end portion of the reflecting surface, and is inclined with respect to the upper surface of the base member; a first bonding film that is a metal film disposed in a region on the upper surface of the base member facing the lower surface of the lateral wall portion; a second bonding film that is a metal film disposed on the lower surface of the lateral wall portion; and a metal bonding member fuse-bonded to the first bonding film and the second bonding film to each other. An end portion of the first bonding film at a reflecting-surface side and an end portion of the second bonding film at the reflecting-surface side are located separately from the lower end portion of the reflecting surface. A distance between the end portion of the first bonding film at the reflecting-surface side and the lower end portion of the reflecting surface is different from a distance between the end portion of the second bonding film at the reflecting-surface side and the lower end portion of the reflecting surface.