A laser includes a wavelength selecting element 14 that selectively reflects laser beams with wavelengths » = » 0 , » 1 , » 2 , ..., » n (n ‰¥ 2) of different laser oscillation modes from among fundamental oscillation wavelengths of laser beams passing through a wavelength conversion element 13, and the wavelength conversion element 13 that converts the laser beams with the wavelengths » = » 0 , » 1 , » 2 , ..., » n (n ‰¥ 2) of different laser oscillation modes reflected by the wavelength selecting element 14 to harmonics. When using a material with a wide gain band as a laser medium 121 of a solid-state laser element 12, a waveguide laser is implemented capable of carrying out high-efficiency wavelength conversion at a plurality of wavelengths within the gain band.