A back light unit includes a light source unit combined with an optical waveguide having translucency to guide a light of light source in a direction of liquid crystal panel, and a chassis for holding or supporting the light source unit. The optical waveguide is formed in plate-like shape, a face opposing to the back face of liquid crystal panel is used as a light emitting surface, a face opposing to the chassis is used as a reflecting face for reflecting a light, one of a plurality of side faces adjacent to light emitting surface and reflecting face is used as a light incidence surface where a light from the light source is injected. The light source unit is arranged in multiple in a horizontal direction or a vertical direction of the liquid crystal panel, in the back face side of the liquid crystal panel.