PURPOSE: To effectively and sufficiently smooth a printing sheet on an impression cylinder by swingably supporting an air flow nozzle at a swinging shaft parallel to an axis of the cylinder as a center, and connecting it to a driving member to conduct a swingingly moving forward and reverse at the time of an operating stroke of a printer.

CONSTITUTION: In order to effectively and sufficiently smooth a printing sheet 1 on a circumference of an impression cylinder 3, air supply nozzles 8 at an interval to a printing gap 5 forward from the gap 5 are directed toward the circumference of the cylinder 3, swingably supported to a swinging shaft 9 as a center. And when a feeding direction of the sheet 1 is observed at the time of an operating stroke of a printer, it is connectible to a driving member 13 to swing forward and backward. The nozzles 8 are constituted as a lead type nozzle. An air flow in a turning angle range β1 is directed toward a rear end of the sheet by turning to a forward position from a return rotated position '0'. Thus, the sheet is raised from the circumference of a conveyor drum 2 and hence not stained.