A control method for a wavelength tunable semiconductor laser device including an active region (2,11a) for oscillating a laser beam, a wavelength tuning region (4,11b) for shifting a wavelength of the laser beam, and a thermal compensation region (4,11c) adjacent to the wavelength tuning region (4,11b) for converting most of the inputted electric power to heat, when a laser beam is oscillated from the wavelength tunable semiconductor laser device, comprising measuring an electric current-voltage characteristic of each of the wavelength tuning region and the thermal compensation region, finding an electric current-electric power characteristic of each of the wavelength tuning region and the thermal compensation region from the electric current-voltage characteristics is disclosed. Further, on the basis of the electric current-voltage characteristics and the electric current-electric power characteristics, determining and controlling an electric current or voltage applied to each of the wavelength tuning region (4,11b) and the thermal compensation region (4,11c) so that the sum of an electric power inputted into the wavelength tuning region and an electric power inputted into the thermal compensation region is always kept constant.