A planar light source device comprising: a plurality of point light; a light guide plate including an incident surface, wherein the light spread out into a planar shape and the light guide plate emits the light from an emitting surface; and a frame including an opening, wherein the frame has a protrusion that is provided on a light source side of a peripheral end portion of the emitting surface of the light guide plate, wherein the point light sources are arranged at the light source side, wherein the protrusion has difference widths parallel to the emitting surface, and wherein a width of a portion of the protrusion, which corresponds to the position where the point of the point light source is arranged, is wider than a width of a portion of the protrusion, which corresponds to a position between the point light sources.