A light source device includes light sources arranged on a substrate in a matrix, and a reflective member. The reflective member includes first walls respectively surrounding the light sources, and defining first regions, and second walls located on an outer side of the first walls, and defining second regions each having an opening facing outside of the reflective member. The reflective member defines a pair of first sides parallel to one of a vertical direction and a lateral direction in a plan view, the pair of first sides being constituted by a part of the reflective member including at least one of the first walls and the first regions, and a second side inclined or curved with respect to the pair of first sides, the second side being constituted by a part of the reflective member including at least one of the second walls and the second regions.