A screw compressor includes a hollow casing inside which a reservoir for air and oil is realized and on which, in an upper position, a suction group for air from outside the reservoir having at least an air intake valve and at least an air filter; on one lateral end a flow block provided with an oil/air separation device and an oil filter and at least a valve for extracting compressed air are disposed. The casing is provided with an opening on the opposite side with respect to that on which the flow block is provided.
The compressor includes a casing closure flange to which a screw compression unit is fixed that when the flange is placed to close the opening causes the insertion into the reservoir of the unit.