A laser oscillator for improving efficiency of conversion from solar rays to laser beams is provided. The laser oscillator includes: a laser medium 31 excited by solar rays to output laser beams; an output mirror 35 having a concave surface 35a opposed to an output end of the laser medium 3i; and a light guide 20 having a reflector 22 extending from the output end of the laser medium 31 tovvards the outside of the laser medium 31 and reflecting the solar rays Sf to guide them to the laser medium 31.
