A screw compressor, comprising: a screw rotor in which a plurality of helical grooves for forming a compression chamber are formed; a casing having a cylinder portion into which the screw rotor is inserted; and an economizer circuit configured to eject intermediate pressure refrigerant into the compression chamber in a course of compression; wherein the economizer circuit includes a branch passage configured to branch the intermediate pressure refrigerant from a portion of a refrigerant circuit that circulates refrigerant and performs a refrigeration cycle, a resonance space connected to a downstream side of the branch passage to retain the intermediate pressure refrigerant, and a resonance passage having an end communicating with an interior of the compression chamber, and the other end communicating with an interior of the resonance space, and characterized in that the screw compressor further comprises an economizer sleeve having a first pipe portion attached to the cylinder portion and communicating with the interior of the compression chamber, and a second pipe portion formed in a shape of a cylinder, the second pipe portion having a diameter larger than a diameter of the first pipe portion, and the second pipe portion having an end connected to the first pipe portion and the other end open to an exterior of the casing; and an economizer flange having a fitted pipe portion fitted into an interior of the second pipe portion, and a flange portion extending radially outwardly from an end of the fitted pipe portion, and wherein the resonance passage is defined by the first pipe portion of the economizer sleeve, the branch passage is defined by the fitted pipe portion of the economizer flange, and the resonance space is a space formed by an inner surface of the second pipe portion of the economizer sleeve, and the fitted pipe portion of the economizer flange. a screw rotor in which a plurality of helical grooves for forming a compression chamber are formed; a casing having a cylinder portion into which the screw rotor is inserted; and an economizer circuit configured to eject intermediate pressure refrigerant into the compression chamber in a course of compression; wherein the economizer circuit includes a branch passage configured to branch the intermediate pressure refrigerant from a portion of a refrigerant circuit that circulates refrigerant and performs a refrigeration cycle, a resonance space connected to a downstream side of the branch passage to retain the intermediate pressure refrigerant, and a resonance passage having an end communicating with an interior of the compression chamber, and the other end communicating with an interior of the resonance space, and characterized in that the screw compressor further comprises an economizer sleeve having a first pipe portion attached to the cylinder portion and communicating with the interior of the compression chamber, and a second pipe portion formed in a shape of a cylinder, the second pipe portion having a diameter larger than a diameter of the first pipe portion, and the second pipe portion having an end connected to the first pipe portion and the other end open to an exterior of the casing; and an economizer flange having a fitted pipe portion fitted into an interior of the second pipe portion, and a flange portion extending radially outwardly from an end of the fitted pipe portion, and wherein a branch passage configured to branch the intermediate pressure refrigerant from a portion of a refrigerant circuit that circulates refrigerant and performs a refrigeration cycle, a resonance space connected to a downstream side of the branch passage to retain the intermediate pressure refrigerant, and a resonance passage having an end communicating with an interior of the compression chamber, and the other end communicating with an interior of the resonance space, and characterized in that the screw compressor further comprises an economizer sleeve having a first pipe portion attached to the cylinder portion and communicating with the interior of the compression chamber, and a second pipe portion formed in a shape of a cylinder, the second pipe portion having a diameter larger than a diameter of the first pipe portion, and the second pipe portion having an end connected to the first pipe portion and the other end open to an exterior of the casing; and an economizer flange having a fitted pipe portion fitted into an interior of the second pipe portion, and a flange portion extending radially outwardly from an end of the fitted pipe portion, and wherein the resonance passage is defined by the first pipe portion of the economizer sleeve, the branch passage is defined by the fitted pipe portion of the economizer flange, and the resonance space is a space formed by an inner surface of the second pipe portion of the economizer sleeve, and the fitted pipe portion of the economizer flange.