An impression cylinder for a rotary printing machine is equipped with outlet orifices for feeding a pressure medium into a slot for the purpose of lifting off a flexible plate from the outer surface of the impression cylinder. The orifice on the circumference of the impression cylinder is inclined in the direction of rotation of the cylinder. The ends of the plate are insertable into the slot and are secured therein against slipping out. The impression cylinder includes a cavity which runs in the longitudinal direction separately from the slot and is capable of being subjected to the pressure medium. The cavity includes at least one duct which is connected to the outlet orifice arranged in a side face of the slot. The side face is adjacent to the trailing end of the plate in the region of the slot orifice on the circumference of the impression cylinder.