At the point in time when it is determined that the number of sheets constituting one sheet bundle exceeds the maximum number of sheets that can be crimp-bound, a sheet bundle that has already been shifted to a crimp-binding position is discharged to a crimp-binding discharge position without being subjected to crimp-binding. Thereafter, succeeding sheets are shifted as a bundle to the crimp-binding position and discharged to the crimp-binding discharge position without being subjected to crimp-binding.