PURPOSE: To stabilize recording power by detecting an amplitude from the pulse modulated beam output of a semiconductor laser as a recording light source by a photodetector and controlling the driving current of the semiconductor laser in the case of recording information corresponding to error compared with a rated value.

CONSTITUTION: A modulation circuit 15 modulates the pulse of the driving current of a semiconductor laser 1 according to a recorded signal, and the pulse modulated beam output is detected by a PIN diode 2, converted by a current/voltage conversion circuit 3 and afterwards amplified by a wide-band video amplifier 4. A differential amplifier 9 calculates difference between positive and negative envelope waveforms obtained from the alternating current component of this signal by positive and negative envelope detection circuits 7 and 8 so as to obtain a signal corresponding to the amplitude of the pulse modulated beam output. As difference between this signal and a recording reference voltage V3, a recording power error signal is obtained by a differential amplifier 10 and corresponding to this signal, a current driving circuit 14 controls the value of the driving current. Thus, against the optical output fluctuation caused by a temperature change or the like, the recording power can be kept at the rated value and stabilized.