A backlight device includes a hot cathode fluorescent tube having a pair of electrodes, a power source arranged to apply voltage having an alternating component to at least one of the pair of electrodes, and an electrode heating circuit arranged to supply heating current to the electrodes. The backlight device further includes temperature sensors that detect the temperatures in the electrodes to be supplied with the heating current. Based on the results detected by the temperature sensors, a switch element is driven by the control section. The heating current is thus controlled. With this, the temperatures in the electrodes of the electrical discharge tube can be more accurately grasped, and the temperatures in the electrodes of the discharge tube can be more properly controlled.