A staple-less binding unit including a pair of upper and lower teeth binds a sheet bundle which is discharged to an intermediate processing tray by a sheet discharge portion and whose one edge abuts against a rear edge stopper. A control portion switches a binding mode of the staple-less binding unit that implements the binding process on the sheet bundle in a first binding mode of binding the sheet bundle without any staple such that the pair of upper and lower teeth bite across an edge of the sheet bundle and in a second binding mode of binding the sheet bundle without any staple such that the pair of upper and lower teeth do not bite across any edge of the sheet bundle.