A backlight device is provided with a substrate whereupon a plurality of light emitting diodes are arranged, and a lower side chassis (heat dissipating unit) where heat generated by the light emitting diodes is transferred from the substrate and dissipated to the outside. An amount of heat generated by each light emitting diode is measured in advance, and in accordance with the measurement results of the amounts of generated heat, an arrangement position on the substrate is determined and corresponding light emitting diodes are arranged.