In order to provide an image forming apparatus capable of maintaining the image quality by making smooth flowability of a surplus developer, which is discharged according to supply of a new developer (toner and carrier), toward a collection box, there are provided a stirring screw that electrify toner by stirring the toner together with a carrier; a casing that supports the stirring screw and stores a developer in which the toner and the carrier are mixed; a inlet used to supply the developer to the casing; a guide that guides the surplus developer discharged from the casing downward; and a reciprocating member that moves on a flow surface of the guide along which the surplus developer flows.