United States LED arrays where a plurality of LEDs are vertically arranged are lit up in luminance corresponding to tone values on digital image data. Light beams in line emitted from the LED arrays are scanned in a horizontal direction to display a two-dimensional image. Clocks A, B, C are selectively gated according to the tone values D0, D1 on the digital image data to generate a drive pulse for driving each of the LEDs on the LED arrays. Each LED thus emits light in luminance corresponding to the tone value on the digital image data. Pulse widths of the clocks A, B, C are changed by one screen. Luminance of each light emitting element corresponding to the tone data on the digital image data is thus changed to increase the substantially representable number of tones.