PURPOSE: To simultaneously realize the high gradation of 1 dot to be requested by a copying machine and the high resolution to be requested by a printer by providing two kinds of information of the information by a clock and plural image data and the information by the on/off signal of an LD as the information on turning on the LD.

CONSTITUTION: A DETP (period detection signal) is delivered to a printer controller 32, the on/off signal (VTHRV) of an LD of 400 to 1200dpi is received in the periodical moment with the signal and the signal as it is outputted to an LD control substrate. As for smoothing, PWM modulations of 2 to 8 stages are used. As the information turning on the LD for the control substrate, the both of the case where LD emitted light quantity is modulated by using a clock and the image data of plural bits and the case of only the on/off signal of the LD. The high gradation of 1 dot to be requested by a copying machine and the high resolution to be requested by a printer can be simultaneously realized and the both of a copying function and a printer function are satisfied.