A data driver used for driving a display panel is provided with a grayscale voltage generator circuit generating a plurality of grayscale voltages; and a drive circuitry selecting a selected grayscale voltage from the plurality of grayscale voltages in response to input display data, and outputting a data signal having a voltage level corresponding to the selected grayscale voltage to the display panel. The grayscale voltage generator circuit comprises an amplifier generating a voltage bias; and a voltage generator circuit generating the plurality of grayscale voltages from the voltage bias. The amplifier is designed so that a polarity of an offset voltage of the amplifier is reversible. The polarity of the offset voltage of the amplifier is controlled so that the polarity of the offset voltage of the amplifier used for driving a specific pixel of the display panel in a certain frame period is opposite to that of the offset voltage of the amplifier used for driving the c specific pixel in another frame period.