To supply drain from a dehumidifier into a compressor body without reducing suction efficiency, and also extend a service life of a lip seal provided at a suction side rotor shaft.

A water-injected screw compressor includes a compressor body 1, an air-water separator 6 separating compressed air and water, ejection passages 19a, 19b leading the compressed air from the air-water separator, body water supply passages 7, 9, 9a returning the water separated by the air-water separator to the compressor body, a dehumidifier 21 provided at the ejection passage, and a drain discharge passage 22 discharging the drain subjected to condensation separation by the dehumidifier. A partition wall 28 is provided at a casing 1A between a lip seal 29 provided at a suction side rotor shaft 3B of the compressor body and a suction side end surface of a rotor tooth part 3A. An axially sealed water injection channel 26 is provided in the partition wall. The drain discharge passage is connected to the axially sealed water injection channel, and the drain is supplied between the lip seal and the suction side end surface of the rotor tooth part.