To increase the light utilization efficiency of a second light source by preventing the generation of a side beam during the use of a second wavelength light source while permitting the generation of a side beam during the use of a first wavelength light source.

A semiconductor laser device 11 is provided with a first light source 1a for emitting a first wavelength light beam, and a second light source 1b for emitting a second wavelength light beam different from the first wavelength light beam. A diffraction grating 12 has a grating groove formed such that its 1st order diffraction efficiency is almost zero for a light beam from the first light source 1a, and a 1st order diffraction light is emitted for a light beam from the second light source 1b.