In a gas compressor, an outline shape of an inner peripheral surface (41) of a cylinder (40) is set such that in a point before a compression chamber (43B) adjacent to a compression chamber (43A) in the upstream side in the rotational direction (W) is exposed to a discharge hole (45b) of a primary discharge portion (45) with rotation of a rotor (50) in the rotational direction (W) (point where the compression chamber (43B) is positioned upstream of an angular position of being exposed to the discharge hole (45b) of the primary discharge portion (45)), a pressure of the refrigerant gas (G) inside the compression chamber (43) reaches a discharge pressure. Therefore the discharge hole (45b) of the primary discharge portion (45) always discherges a refrigerant gas (G) from the compression chamber (43) to prevent generation of the discharge pulsation.
