Included are a light-emitting circuit having a laser diode (LD); an LD drive circuit for driving the light-emitting circuit; a bias circuit for adding a bias current to a pulse current outputted from the LD drive circuit; a light-receiving circuit for receiving monitoring light outputted from the light-emitting circuit; an I/V conversion circuit for subjecting an output from the light-receiving circuit to current-to-voltage conversion; a maximum-value detection circuit and an average-value detection circuit for respectively detecting the maximum and minimum values of an output voltage of the I/V conversion circuit; a first comparator for comparing the detected maximum value with a first reference value to feed back the comparison result to the LD drive circuit; and a second comparator for comparing the detected average value with a second reference value to feed back the comparison result to the bias circuit.