When a light source of a first wavelength is used, side beams are allowed to occur, whereas side beams are prevented from occurring when a light source of a second wavelength is used, thereby raising the light use efficiency of the second light source. A semiconductor laser device comprises a first light source for emitting a light beam of a first wavelength and a second light source for emitting a light beam of a second wavelength different from the first wavelength. The grading groove of a diffraction grating is so formed that the first-order diffraction efficiency is almost zero for the light beam from the first light source and the first-order diffraction light is emitted for the light beam from the second light source.