A backlight unit is provided. The backlight unit includes an LED; an LED driving unit which drives the LED in accordance with a switching operation of a transistor; and a control unit which adds an additional signal to an output current of the LED to obtain a combined current, compares the combined current with the reference current, and controls the switching operation of the transistor based on the results of the comparison, wherein the additional signal is a current signal whose level increases over time in each period and is then reset to a predefined value in each period in accordance with an operation cycle of the transistor.