A screw compressor includes a pair of male and female screw rotors which meshes with each other, where a casing storing the pair of screw rotors is divided into a discharge opening neighborhood portion including at least a discharge opening and an other portion other than the discharge opening neighborhood portion, the discharge opening neighborhood portion is configured so as to be removable from the other portion, further, the casing is divided, by two dividing surfaces orthogonal to rotor shafts, into three portions including a rotor casing around the pair of screw rotors, a discharge casing on a side of the discharge opening, and a suction casing on a side of a suction opening, and the discharge opening neighborhood portion is formed by dividing the rotor casing, and is configured so as to be removable from the dividing surface on the side of the discharge opening of a divided rotor casing. According to this configuration, the number of man-hours required for production thereof is reduced, and if operation conditions change, the size of a discharge opening can be easily changed.