A semiconductor laser optical output control circuit able to precisely control an optical output of a semiconductor laser, provided with a peak value detection circuit 106-1 and a bottom value detection circuit 107-1 for detecting the output of a photo-diode PD 102, optical power setting voltage sources 105-1 and 105-2 for giving the setting value of the optical output of a semiconductor laser LD 101, a peak value detection circuit 106-2 and a bottom value detection circuit 107-2 for detecting the output of a switching circuit 104 for switching the setting value, error amplifiers 108-1 and 108-2 for comparing the detected outputs of the peak value detection circuit 106-1 and peak value detection circuit 106-2 and the bottom value detection circuit 107-1 and bottom value detection circuit 107-2, and a switching circuit 110 for switching the comparison results of the error amplifiers 108-1 and 108-2 and supplying the same to a current amplifier 111 in synchronization with the switching circuit 104.