A gas compressor includes a cylinder member, a rotor, and a plurality of vanes, wherein a proximal section is provided between the cylinder member and the rotor, so that a single cylinder room which performs a refrigerant gas compression cycle one-time per one rotation of the rotor is defined, and at least one sub-discharge section which maintains pressure of the refrigerant gas in a compression room in discharge pressure by releasing pressure of the compression room when the pressure of the refrigerant gas in the compression room reaches the discharge pressure.