A semiconductor laser device assembly includes (A) a semiconductor laser element and (B) a diffraction grating that configures an external resonator, returns diffraction light other than zero-th order diffraction light to the semiconductor laser element, and outputs the zero-th order diffraction light to the outside. An extension direction of a diffraction surface of the diffraction grating and a main vibration direction of a field of a laser beam incident on the diffraction grating are substantially parallel to each other.