a sheet post - treatment apparatus with a sorting apparatus for containing sheets discharged in a plurality of sort bins , a connecting unit for introducing sheets discharged into the sorting apparatus , a sheet discharge tray for use in a non - sort mode provided independently of the sorting apparatus for piling thereon the sheets discharged , and a changeover device for selectively changing over bewteen a first mode for introducing the sheets discharged into the sorting apparatus through the connecting unit , and a second mode for introducing the sheets into the sheet discharge tray when in a non - sort mode .