The present invention is to provide a sheet discharge device capable of preventing the lowermost sheet on a tray from being displaced. A present sheet post-processing device includes a first tray for stacking a sheet, a processing tray that temporarily stacks conveyed sheets until a number of the sheets reaches a predetermined number, and a discharge mechanism that discharges the sheets stacked on the processing tray onto the first tray. A sheet bundle forming unit divides, when forming a first sheet bundle on the first tray, sheets constituting the first sheet bundle into a plurality of sets and discharges the sheets a plurality of times for each set. At this time, a number of sheets included in a sheet set to be discharged at the first time is smaller than a maximum number of sheets included in sheet sets to be discharged at the second and subsequent times.