To perform double-side printing by sheet braking by an air jet at a suitable timing during a period from when a printing sheet is released from a chain gripper at a certain angle from forward vertical directions of the sheet to when the sheet is brought into contact with a sheet guide, thereby eliminating a vacuum wheel.

An inertial speed of a printing sheet P is braked by an air jet of an air jet nozzle 9 at an angle from vertical directions at a suitable timing during a period from when the sheet P is released from a chain gripper 1 to when the sheet P is brought into contact with a sheet guide 5. As a result, the sheets P are regularly stacked and aligned on a delivery sheet base 6. Air jet pressures in vertical, lateral and oblique directions of the air jet are regulated according to a speed change of the sheet P. Thus, since no vacuum wheel is used, the overall sheet can be printed without contaminating a rear surface of the sheet.