Light source device

A light source device comprising:

• one or more reflective members having a plurality of reflective surfaces including a first reflective surface and a second reflective surface;
• a plurality of light-emitting elements including a first light-emitting element emitting first light that travels in a direction in which the reflective member is arranged to be incident on the first reflective surface, and a second light-emitting element emitting second light that travels in a direction in which the reflective member is arranged to be incident on the second reflective surface;
• and
• a first photodetector having a first light-receiving surface on which the first light that travels in the direction in which the reflective member is arranged and is transmitted through a transmissive region that is present between the first reflective surface and the second reflective surface and that transmits the first light more than the first reflective surface is irradiated,
• wherein the one or more reflective members are immovably fixed relative to the plurality of light emitting elements and the first photodetector.