A gas laser oscillator includes a discharge section for exciting laser gas, a blowing section for transmitting the laser gas, and a laser gas flowing path for forming a circulation route of the laser gas between the discharge section and the blowing section. The blowing section is formed of a rotary part to be rotated by a shaft driver and a non-rotary part not to be rotated. The rotary part includes a rotary shaft to which an impeller is mounted at an end, the shaft driver for rotating the rotary shaft, an upper bearing and a lower bearing coupled to the rotary shaft. The rotary part is detachable from the non-rotary part.