A display device operating in accordance with a sub-field process, includes a first block which varies the number of bits of a received image signal, a second block which calculates an average picture level (APL) of images defined by the image signal transmitted from the first block, a third block which converts the image signal into sub-field coding data, and outputs the sub-field coding data to a display panel, and a fourth block which receives the average picture level from the second block, converts the received average picture level to the number of sustaining pulses, transmits the number of sustaining pulses to the display panel, and transmits the number of sustaining pulses to the third block, wherein the third block selects the number of bits of a signal to be input thereinto, in accordance with the number of sustaining pulses received from the fourth block.