A light source device includes a surface emitting laser, a surface emitting laser holding unit on which the surface emitting laser is mounted, a parallel plate that is arranged on a light path of a light flux from the surface emitting laser so that the light flux enters into one surface thereof, and that is made of a transparent material, and a holder having a through hole that functions as a light path of the light flux from the surface emitting laser, wherein the surface emitting laser holding unit is brought into contact with the holder, the parallel plate is fixedly bonded to the holder, and a part of the through hole of the holder is sealed with the surface emitting laser holding unit and the parallel plate.