A controller stores image signals Sp represented as binary values for every unit of frame. The controller divides one frame into a plurality of sub-frames representing an image by image data of two gradation levels, in accordance with respective figures of the stored image signals Sp for one frame. The image data of two gradation levels for each of the sub-frames is written into capacitors Cp from a drain driver, for every row. When the image data is "1", a drive transistor is turned on. A common driver applies a voltage of a predetermined level for every sub-frame, to control the voltage applied between electrodes of an organic EL element. As a result, the organic EL element emit light with brightness which differs between sub-frames. Images of the sub-frames are visually synthesized, so that gradation is expressed in one frame.