PURPOSE: To restrict the installation area small, and prevent the happening of trouble due to a collision by eliminating a discharged paper tray projected to the side of an after-treatment device main body.

CONSTITUTION: A device for after-treatment of paper is provided with a stapler 4 for aligning paper bundles, on which an image is already formed and which is discharged from an image forming device, to staple them and a guide member 6 for carrying and guiding the stapled paper bundle toward a paper discharging unit. A loading table 8 to be loaded with paper bundle is provided on the top surface of the after-treatment device main body 2, and a guide member 6 is arranged between the loading table 8 and the stapler 4 so as to be stood in outline.