It is provided system and method of oscillating blue laser beam having a relatively high conversion efficiency and whose output power of the blue laser beam can be improved. Light emitted from a broad area semiconductor laser device 2 of Fabry-Perot type is irradiated into a slab optical waveguide 8 made of a non-linear optical crystal as a fundamental wave “A”. Blue laser beam “B” is emitted from the slab optical waveguide 8.