A semiconductor laser wavelength control device capable of controlling the optical wavelength constant even if the optical output intensity of the semiconductor laser varies and permitting a reduction in overall size is to be provided.It is provided with control means which controls the optical wavelength of a laser diode 1 to a prescribed wavelength by driving a temperature control unit to control the temperature of the laser diode 1. The control means has a low pass characteristic, with a first photo electric conversion signal resulting from the conversion of light having passed an optical filter 7 into an electric signal and a target for the laser diode 1 to emit light of a prescribed wavelength being entered as inputs, supplies a control signal for driving the temperature of the temperature control unit, and is set that a greater one out of a plurality of poles has a higher frequency than the cut-off frequency f.sub.c and the zero point has a lower frequency than the cut-off frequency f.sub.c of the object of control.