A display device with reduced power consumption has pixels coupled with data lines and arranged in a matrix, a signal controller processing input image signals and outputting output image signals, and a data driver applying data voltages, corresponding to output image signals, to the data lines. When all the input image signals have either a first or second value, the output image signals have the first value. The signal controller generates a polarity signal for determining data voltage polarity, and when all the input image signals have either a first or second value, data voltages corresponding to the input image signals have a polarity equivalent to a polarity of previously applied data voltages. The signal controller generates a control signal for controlling the data driver's clock synchronization circuit, and the control signal halts the clock synchronization circuit when an operating frequency is lower than a predetermined value.