To provide a paper sheet post-processing device capable of impairing no stacking property of bundles of the delivered paper sheets in the case of repeating delivery/stacking of a plurality of bundles of the sheets without forcibly limiting the stackable number of bundles (in detail, the number of Z-folded paper sheets contained in the bundles to be stacked).

In the paper sheet post-processing device for folding, stitching and sorting the paper sheets delivered after transference of images from an image forming device structuring an image forming system in order, a plurality of vertically movable paper sheet delivery trays for stacking the paper sheets are provided in an upper part and a lower part, and a guide member 43 for guiding bundles of the paper sheets delivered onto the lower stage side of the plurality of paper sheets delivery trays 10 and 11 is provided in the upper stage side delivery tray out of the plurality of paper sheet delivery trays 10 and 11.