A light-emitting-diode backlight device includes a light source substrate to which many light-emitting diodes are mounted, and a bottom chassis having the light source substrate mounted to a principal surface side of the bottom chassis. Illumination light from the light-emitting diodes is supplied to a display panel unit. A back-surface side of the bottom chassis is provided with a heat-dissipating unit making uniform a temperature distribution over the entire bottom chassis. The heat-dissipating unit includes a mounting plate, a heat pipe, and a radiating fin. The mounting plate is mounted to at least a high-temperature area of the bottom chassis. The heat pipe is disposed on both the high-temperature area and a low-temperature area, and is mounted to the mounting plate. The radiating fin is mounted to the low-temperature area, and connected to an end of the heat pipe.