Image data are inputted from a data processing means (23) into storage means (24) so that light emitting elements on one line (28a) of a light emitting element (yellow) line head (28) are actuated according to signal outputted from a shift resistor (24a) so as to expose pixels on an image carrier. At a point of time when the pixels reach a position corresponding to the light emitting elements in a next line (28b) by moving the image carrier in a direction of arrow X, the image data are transmitted to a shift resistor (24b) and then outputted to the line (28b) so as to expose the pixels again. The image data are transmitted among the shift resistors sequentially by moving the image carrier, thereby achieving the multiple exposure of the same pixels.