To provide a paper post-processing apparatus improving the quality of a booklet by stabilizing conveyance of the booklet by retreating a conveying member with a large friction coefficient and allowing the booklet to slide on another supporting member to reduce the frictional force of conveyance when the booklet is positioned on a cutting device.

The booklet 25 folded at the center by the post-processing device 9 is conveyed to the slightly downstream side of a cutting position by the conveying member 44a, and drive of the conveying member 44a is stopped. The upper surface of the conveying member 44a is lowered below the upper surface of the supporting member 44c and stopped, and the booklet 25 is allowed to be supported by the supporting member 44c. An abutting member 44b is lowered below a contact surface between the booklet 25 and the supporting member 44c. The abutting member 44b is then moved to the upstream side in the conveying direction and is brought into contact with the center-folded face of the booklet 25. Further, the booklet 25 is allowed to slide and move to the cutting position while adjusting the posture, by which positioning is carried out without sliding on the conveying member with the large friction coefficient.