Provided is a display device capable of brightness adjustment by adjusting gamma curves thereof, without adjusting brightness of input video signals. The display device includes a memory unit, storing a plurality of gamma reference voltage value sets in accordance with a plurality of gamma curves; a microprocessor, for selecting one of the gamma reference voltage value sets stored in the memory unit; a gamma voltage generator, for generating a plurality of gamma reference voltages in response to the selected gamma reference voltage value set from the microprocessor; a data converter, for converting input video signals into video voltages in response to the gamma reference voltages provided from the gamma voltage generator; and a display panel, for displaying images in response to the video voltages from the data converter.