PURPOSE: To take out treated paper sheets without touching paper sheets under treating, by stacking paper sheets under staple treatment extending over an auxiliary plate and a staple plate, while stacking bookbinding paper sheets, which is completed staple treatment, on an discharge tray.

CONSTITUTION: A post-treatment device 1 for paper sheets is provided with a post-treatment means 3 which adjusts paper sheets conveyed from a post- treatment conveyance path 2 and staple treats so as to be bound into a book, a discharge means 4 for discharging bound paper sheets, etc. In this case, a paper extrusion member 13 is attachedly provided with an extrusion belt 16 which is arranged parallel under a staple plate 8 having a paper discharge roller 14 on its upper end and an auxiliary plate 5 moving in its reverse direction. At staple treatment, the auxiliary plate 5 is arranged in the upper part of a discharge tray 26 so that paper sheets are stacked extending over the auxiliary plate 5 and the staple plate 8. In discharging bookbinding paper sheets, the auxiliary plate 5 is stored in a downward position of the staple plate 8.