PURPOSE: To simplify a sheet post-treatment device so as to aim at lowering the cost of the device by leading a push-out member to a guide member in a bin above a bin on which sheet bundles are stacked, so as to push out a bundle of sheets, thereby it is possible to shorten the time of conveyance of a sheet bundle.

CONSTITUTION: If a sheet bundle S is conveyed from a sorter to a storage device, after sheet bundles S are stapled by means of a stapler, a control section allows a drive means to lower bins 17 by one stage, respectively. Further, after completion of the shift of the bins 17, the control section allows a motor M to rotate a pinion 27 so as to lead a push-out member 25 to a guide member 30 in the direction of the arrow A. With this arrangement, the sheet bundles S are stacked on a bin 17 which is located at a position B2, and the stapled sheet bundles S are pushed out onto a pair of grip belts by the push-out member 25. Accordingly, the conveying time of the sheet bundles are shortened so as to cope with a high speed machine, and the device 1 may be simplified to aim at lowering the cost thereof.