A flat display device includes a flat panel including a plurality of gate lines; a first gate driving portion connected to odd gate lines among the plurality of gate lines; a second gate driving portion connected to even gate lines among the plurality of gate lines; a driving mode selection portion generating a driving mode signal corresponding to source output inputted thereto; and a timing control portion operating in a moving image mode or a still image mode in response to the driving mode signal, wherein the first and second gate driving portions alternately operate per a frame in the still image mode, or wherein the first and second gate driving portions alternately operate per a field in the moving image mode, in which the field is shorter than the frame.