It has a gradation voltage generation circuit 1 for generating a plurality of voltage values suited to gamma characteristics of a liquid crystal and so on, a digital image data storage circuit 3 for storing digital image data displayed on a display device, a gradation voltage selection circuit 2 for selecting one value according to digital data stored by the digital image data storage circuit 3 from the plurality of voltage values generated by the gradation voltage generation circuit 1, an amplifier 4 for receiving a voltage selected according to the digital image data and driving a data line of the liquid crystal and so on at a predetermined voltage, a voltage detection circuit 7 for detecting voltage variations of the amplifier 4, a correction data storage circuit 6 for storing a state of the voltage variations of the amplifier 4, and a voltage correction circuit 5 for correcting output voltage variations of the amplifier 4.