An image forming apparatus includes an image bearing member for bearing an electrostatic image; a developer carrying member for carrying a developer and for forming a developing zone with the image bearing member, wherein the developer is externally added with additive having a charging polarity opposite from that of the developer; voltage applying means for applying a developing voltage to the developer carrying member; voltage control means for controlling the developing voltage so as to change force for directing the additive toward a non-image portion of the image bearing member in accordance with a number of image forming operations.