When performing gradation display by giving digital value as display data to each pixel arranged in a matrix on a display panel and emitting the pixels at a brightness corresponding to the magnitude of the digital value, plural display frame periods are set as one cycle, and digital value α is given as display data in certain display frames selectively determined in the cycle, and digital value β = α ± M (M being a positive integer) is given as display data in other display frames in the same cycle. Accordingly, a halftone gradation between the gradation corresponding to the digital value α and the gradation corresponding to the digital value β may be displayed in plural degrees depending on the rate of the number of display frames given the digital value α and the number of display frames given the digital value β.