PURPOSE: To improve the stability of temperature to pulse width photoelectrically converted besides the stability of temperature to the optical output, and to utilize the control circuit for the laser driving circuit of a beam transmitter by making the DC bias currents of the laser-diode constant and changing the amplitude of pulse currents.

CONSTITUTION: The photoelectrically converted output of a photo-diode PD is levelled bymeans of a capacitor C1, and amplified by means of an operational amplifier A1, and the output is compred with fixed voltage supplied by a variable resistor Rv1 by means of an operational amplifier A2 and amplified. The variable resistor Rv1 by means of an operational amplifier A2 and amplified. The variable resistor Rv1 functions as the setting of the amplitude of the pulse currents of the laser-diode. CCP is formed by an operational amplifier A3, a transistor TR3 and a resistor R6, and supplies currents proportional to APC output to the laser-diode LD through a high-speed switching circuit SW. CCB is formed by a variable resistor Rv2, an operational amplifier A4, a transistor TR4 and a resistor R7, and supplies DC bias currents IB proportional to voltage fed from the variable resistor Rv2 to the laser-diode LD.