A post-processing apparatus configured to collect printed sheets ejected from an image forming apparatus and to handle the printed sheets. The post-processing apparatus has: a stacker configured to collect and stack a plurality of printed sheets with one end of each of the printed sheets placed down; a movable stopper configured to stop each of the printed sheets sliding down in the stacker at a specified position; a motor configured to move the stopper along the stacker and stops the stopper; and a control unit configured to control the motor. The control unit increases a current supplied to the motor in preparation for a collision between each of the printed sheets and the stopper.