Abstract: In a reciprocating piston air compressor, air is induced via an intake valve in the compressor cylinder head and, in addition, air which has been pre-compressed on the rear side of the piston is forced into the cylinder space via slots in the cylinder wall controlled by the piston. The delivery and the efficiency of the air compressor are improved according to the invention by the provision that the pre-compression of the air occurs by means of a turbo-compressor and that during the return stroke of the piston, the cylinder space is connected with an additional clearance space via an opened control valve in the cylinder head, by means of which the hot compressed air which has not been expelled is replaced by cooler air.