The direct-type backlight device of the present invention includes a reflecting plate, a plurality of point light sources and a light diffusing plate in this order. A light emitting surface of the light diffusing plate is provided with a fine concavo-convex structure which is a split image forming member. By the fine concavo-convex structure, images A1, B1, C1 and D1 on the light emitting surface corresponding to four point light sources A, B, C and D which constitute a convex quadrilateral which has the smallest area and the shortest circumference length among the plurality of point light sources are observed in a specific region W in a region surrounded by positions A0, B0, C0 and D0 which are positions of the projected image of the point light sources A, B, C and D on the light diffusing plate.