To enable a bunch of sheets to be reliably discharged to a stack tray, also in the case where weight of the bunch of sheets formed on a processing tray is large, a post-processing control section receives information on an ink discharge amount, the number of sheets, sheet type, and printing mode (two-side/one-side) in printing on sheets from a main body control section of an image forming unit A, in forming a bunch of sheets on the processing tray. The control section thereby recognizes weight of a bunch of sheets formed on the processing tray, and when the section determines that the weight is heavier than predetermined weight, decreases a rotation velocity of a drive motor of a sheet bunch transport means, or increases a current amount applied to the drive motor. By this means, torque of the motor is increased, and the bunch of sheets is reliably discharged to the first stack tray.

To enable a bunch of sheets to be reliably discharged to a stack tray, also in the case where weight of the bunch of sheets formed on a processing tray is large, a post-processing control section receives information on an ink discharge amount, the number of sheets, sheet type, and printing mode (two-side/one-side) in printing on sheets from a main body control section of an image forming unit A, in forming a bunch of sheets on the processing tray. The control section thereby recognizes weight of a bunch of sheets formed on the processing tray, and when the section determines that the weight is heavier than predetermined weight, decreases a rotation velocity of a drive motor of a sheet bunch transport means, or increases a current amount applied to the drive motor. By this means, torque of the motor is increased, and the bunch of sheets is reliably discharged to the first stack tray.