A modulation clock supplied to a drive circuit (7) of a display panel (1) is frequency-modulated so as to spread its harmonics spectrum. The frequency deviation is so restricted that, if at least two pixels corresponding to two adjacent scanning wirings are displayed based on arbitrary same luminance data, a difference in display luminance in a specified period between one pixel and the other pixel is less than or equal to a tolerable value determined by the luminance data. Consequently, reduction in unnecessary radiation can be achieved at a lower cost while suppressing deterioration in image quality