A backlight unit includes: light sources; a light guide member (120) arranged at a prescribed gap to the light sources such that light from the light sources enters from respective side faces (121) and exits from a light exiting surface (122); a first extending part (181) that extends along the side face (121) of the light guide member (120); and a second extending part (182) that extends along a surface of the light guide member (120) that is opposite to the light exiting surface (122). The backlight unit is provided with heat dissipation plates (180) that dissipate heat generated by the light sources. Each heat dissipation plate (180) has a larger area at the top portion than the bottom portion when the backlight unit is installed in a liquid crystal display device (1).