A multi wavelength laser device comprising: a pumping light source configured to emit a plurality of pumping lights for providing gains for laser media; the multi wavelength laser device comprising the laser media that have respective end portions on a side of said pumping light source, said end portions being configured to allow said pumping lights to pass therethrough and to reflect a plurality of laser lights having fundamental wavelengths, the laser media further being configured to perform optical amplification by using said plurality of pumping lights emitted from said pumping light source and to emit the plurality of laser lights whose fundamental wavelengths differ from one another; a dispersing element configured to change a traveling direction of each of said plurality of laser lights emitted from said laser media according to the fundamental wavelength and an incidence direction, and to emit said plurality of laser lights in a state in which said plurality of laser lights are superposed on same axis; an angle adjustment mechanism configured to adjust angles of incidence of said plurality of laser lights incident upon the dispersing element; a wavelength conversion element that has a plurality of sets of polarization layers disposed therein, wherein each set of polarization layers consists of polarization inverted regions and polarization non-inverted regions the sets having different periods, and wherein the period of each set of the polarization inverted regions and the polarization non-inverted regions is determined according to the wavelengths of the incident fundamental wave laser lights, the wavelength conversion element being configured to perform wavelength conversion, in said sets of polarization layers having different periods, on said plurality of laser lights emitted from said dispersing element and placed in the state in which said plurality of laser lights are superposed on said same axis, and to emit a plurality of laser lights acquired through said wavelength conversion in a state in which said plurality of laser lights are superposed on same axis; and a mirror configured to construct resonators for said plurality of laser lights whose fundamental wavelengths differ from one another, together with said end portions of said laser media on the side of said pumping light source, the mirror being configured to allow the plurality of laser lights emitted from said wavelength conversion element and acquired through said wavelength conversion to pass therethrough, and to reflect said plurality of laser lights whose fundamental wavelengths differ from one another. a pumping light source configured to emit a plurality of pumping lights for providing gains for laser media; the multi wavelength laser device comprising the laser media that have respective end portions on a side of said pumping light source, said end portions being configured to allow said pumping lights to pass therethrough and to reflect a plurality of laser lights having fundamental wavelengths, the laser media further being configured to perform optical amplification by using said plurality of pumping lights emitted from said pumping light source and to emit the plurality of laser lights whose fundamental wavelengths differ from one another; a dispersing element configured to change a traveling direction of each of said plurality of laser lights emitted from said laser media according to the fundamental wavelength and an incidence direction, and to emit said plurality of laser lights in a state in which said plurality of laser lights are superposed on same axis; an angle adjustment mechanism configured to adjust angles of incidence of said plurality of laser lights incident upon the dispersing element; a wavelength conversion element that has a plurality of sets of polarization layers disposed therein, wherein each set of polarization layers consists of polarization inverted regions and polarization non-inverted regions the sets having different periods, and wherein the period of each set of the polarization inverted regions and the polarization non-inverted regions is determined according to the wavelengths of the incident fundamental wave laser lights, the wavelength conversion element being configured to perform wavelength conversion, in said sets of polarization layers having different periods, on said plurality of laser lights emitted from said dispersing element and placed in the state in which said plurality of laser lights are superposed on said same axis, and to emit a plurality of laser lights acquired through said wavelength conversion in a state in which said plurality of laser lights are superposed on same axis; and a mirror configured to construct resonators for said plurality of laser lights whose fundamental wavelengths differ from one another, together with said end portions of said laser media on the side of said pumping light source, the mirror being configured to allow the plurality of laser lights emitted from said wavelength conversion element and acquired through said wavelength conversion to pass therethrough, and to reflect said plurality of laser lights whose fundamental wavelengths differ from one another.