Sheet processing device incuding a stacked-sheet-count limiting unit configured to limit the number of sheets holdable in the sheet tray and image forming system

A sheet processing device for binding a plurality of sheets together, the sheet processing device comprising:

• a plurality of binding units differing from each other in maximum sheet count, the maximum sheet count being a maximum number of sheets bindable at one time;
• a sheet tray configured to hold sheets until all to-be-bound sheets are placed therein, the number of the to-be-bound sheets being equal to or smaller than a largest one of the maximum sheet counts of the plurality of binding units;
• and
• a stacked-sheet-count limiting unit situated in a thickness direction of the sheets held in the sheet tray, the stacked-sheet-count limiting unit being configured to limit the number of sheets holdable in the sheet tray by being configured to vary a distance in a sheet thickness direction from a sheet support surface of the sheet tray on which the to-be-bound sheets are placed, the distance being based upon the maximum sheet count of the one of the binding units by which the plurality of to-be-bound sheets in the sheet tray are to be bound.