PURPOSE: To enable pixel signals to be processed at low cost by providing a storage means with such a construction that pixel signals for a plurality of lines can be stored at each bit therein, and reading the plurality of pixel signal corresponding to the plurality of lines from each bit.

CONSTITUTION: An image signal VDO1 inputted sequentially is inputted into a bit 0 in a memory 65 through a 3-state latch 64, and an address counter 66 is incremented by the leading edge of an image clock signal VCLK2 to enter a reading mode. A discriminating circuit 20 decides whether a pixel in question is a pixel to be provided with a dot and also a size into which the dot is to be reproduced, based on data corresponding to the pixel in question and the surrounding pixel. A PWM circuit 23 outputs a pulse width modulation signal to a laser driver 25, based on signals 21, 22 inputted from the discriminating circuit 20. When the signal 21 designates formation of a dot and the signal 22 designates a dot smaller than a normal size, the circuit 23 outputs a pulse signal with a pulse width smaller than a predetermined width.