A semiconductor laser 10 has a plurality of wavelength selection portions having a different wavelength property from each other and is mounted on a temperature control device 20. The laser is controlled by a first step of correcting the temperature of the temperature control device 20 according to the detected output wavelength of the semiconductor laser; and a second step of controlling at least one of the wavelength selection portions so that changing differentials amount between the wavelength property of each wavelength selection portion is reduced, the changing differential amount being caused by a temperature correction of the temperature control device. This ensures that the two spectra do not become misaligned as a result of the temperature correction.
