In a gas compressor, housing heads are disposed to define an internal space with a housing, and two rotors housed in the internal space are rotatable to form in the internal space a compression chamber. The housing has an inner wall surface opposed to at least outer peripheral surfaces of the two rotors, and the housing heads are provided in correspondence to the respective rotors. One end portion of a rotary shaft of each rotor is supported by the housing, and other end portion of the rotary shaft of each rotor is supported by the housing heads. The housing heads have a first outer peripheral portion corresponding to the inner wall surface of the housing, and a second outer peripheral portion larger than the first outer peripheral portion. Furthermore, the first outer peripheral portion of the housing heads is fitted onto the inner wall surface of the housing.