Abstract: A casing of a screw compressor has a delivery inner wall face facing delivery end faces of a male rotor and a female rotor. The delivery inner wall face of the casing has a shield area that shields at least a part of a track of an axial fluid communication path, which is a clearance that periodically occurs at the delivery end faces according to variation of intermeshing of the male and female rotors upon rotation thereof and is bounded by trailing flanks of the male and female rotors. The shield area of the casing is provided with a groove group made up of a plurality of grooves having longitudinal directions. The grooves of the groove group are juxtaposed in the circumferential direction of at least one rotor of the male and female rotors and are arranged such that their sides extending in the longitudinal directions are disposed adjacent to each other.