Abstract: A gas laser oscillator has at least a partial reflection unit and a total reflection unit, each of which comprises an extension unit for connecting between a gas introducing unit and a fixed block unit. The gas introducing unit has a gas inlet port for circulating laser gas in a laser tube, and the fixed block unit is provided for fixing a reflector. A gas inlet port of the gas introducing unit is arranged with a predetermined interval of 120 mm or more so that the reflectors are free from contamination by floating powders and deterioration by ultraviolet lays.