A backlight unit 12 includes a chassis 14, an LED 17, a light guide plate 19, a duct member 22, and dissipative LED attachment portion 30. The chassis 14 includes a light exit portion 14c through which light exits. The LED 17 is arranged close to an end portion of the chassis 14. The light guide plate 19 is arranged closer to a middle area of the chassis 14 than the LED 17 and light from the LED 17 is guided toward the light exit portion 14c thereby. The duct member 22 is arranged on the side opposite to the light exit portion 14c side of the chassis 14 and has an air passage 23 therein. The duct member 22 is formed of a composite plate 37 including a resin core 38 having a plate-like shape and a pair of metal plates 39 and 40 arranged so as to sandwich the resin core 38 from a front side and a rear side. The dissipative LED attachment portion 30 is provided to the duct member 22 and includes one part facing the air passage 23 and another part protruding to inside of the chassis 14 and to which the LED 17 is attached.