PURPOSE:To oscillate the fundamental wave of a desired output light with simple constitution, by forming a solid laser crystal in a wedge type wherein an outer end surface and an inner end surface are intersecting. CONSTITUTION:An optical wavelength conversion apparatus 16 consists of the following; a wedge type Nd-doped YAG laser crystal 13 irradiated with pumping laser light, an output mirror 14 and an end surface mirror formed on the pumping laser light incidence end surface 13A whose mirrors resonate laser light, and a KNbO3 crystal 15 which outputs the second harmonic wave form the inputted fundamental wave. The inclination of a second end surface 13B to a path 21 is so adjusted that the angle of refraction of laser light whose wavelength is to be oscillated becomes equal to the wedge angle theta1 (crossing angle of a first end surface 13A and the second end surface 13B) of the YAG laser crystal 13. Thereby only the laser light of desired wavelength is normally reflected by the end surface mirror of the second end surface 13B.