A light source device includes first and second surface light sources, a first optical system that forms light source images of the first and second surface light sources on an image forming surface, an optical element provided with a columnar light guide section, and a second optical system that forms, on an entrance surface of the light guide section, an image of a synthesis surface light source comprising the light source images of the first and second surface light sources. The first optical system includes a reflection element provided with a first reflection surface that reflects a first light flux from the first surface light source toward the image forming surface, and a second reflection surface that reflects a second light flux from the second surface light source toward the image forming surface and that is at right angles to the first reflection surface.