A cartridge assembly for an image forming apparatus, including a drum unit provided with a waste toner conveyor which conveys waste toner collected from a surface of a photosensitive drum to one side; a developing unit connected with the drum unit, configured to receive the waste toner collected from the drum unit, and having a developer discharger to discharge a developer therein to an outside; and a developer collecting unit integrally formed with the drum unit at one side of the drum unit, and configured to collect the developer discharged by the developer discharger of the developing unit, wherein the drum unit includes a toner injector which connects the waste toner conveyor, a new toner supply unit and the developing unit so that the waste toner conveyed by the waste toner conveyor and new toner supplied from the new toner supply unit are injected together into the developing unit.