To provide a light source device enabled not to generate squeaking noise between a clip and a reflective sheet, when they are thermally expanded.

The light source device is provided with a case 2 equipped with a plurality of first holes 23 at a wall part to be opposed to a lamp 1 housed, a reflective sheet 3 equipped with a plurality of second holes 31 corresponding to the first holes 23 to reflex light emitted by the lamp 1, and a clip 4 equipped with a locking part 41 locked to the wall part by being inserted into the first holes 23 and the second holes 31 and a holder part 42 holding the lamp 1. It is also provided with a convex part 5 regulating movement of the clip 4 toward a side of the wall part at least at either the wall part or the clip 4 by being in contact with the other when the locking part 41 is locked to the wall part, and a distance H between the wall part and the holding part 42 is to be kept at not more than a thickness of the reflective sheet 3.