A backlight unit includes: light guide plate surrounded by main surfaces and end surfaces, one end surface facing a light source designated as entrance surface, one main surface designated as emitting surface; first prism sheet provided above the light guide plate, having first prism columns on a top surface and second prism columns on a bottom surface, each first prism column has first ridge line parallel or perpendicular to the entrance surface, each second prism column has second ridge line extending in a different direction from the first ridge line; second prism sheet provided above the first prism sheet, having third prism columns abutting each other on a top surface, each third prism column has third ridge line extending in a direction different from the first and second ridge lines; and reflection sheet facing the light guide plate below the light guide plate.