In a perforating apparatus which has a holder to which a perforating blade can be fastened, the perforation is produced via the movement of a piston by the piston pressing against an air cushion, which in turn transmits this pressure to a perforating piston which presses the perforating blade downward. A positioning device which directly varies the position of the piston unit relative to the housing surface is provided for the zero setting of the piston.