A light source device includes: a first reflector having a first reflective surface; a second reflector having a second reflective surface that is parallel to the first reflective surface and is located in a space behind the first reflective surface with respect to a normal direction of the first reflective surface; a first light source that emits a first light beam directed to the first reflective surface; and a second light source emitting a second light beam that is parallel to the first light beam. The second light beam is directed to the second reflective surface through a space in front of the first reflective surface.