An image forming apparatus capable of preventing the increase of the size thereof by having a lengthened developer bearing member is provided with regard to an image forming apparatus capable of printing a registration mark (dragonfly) on a large sheet of recording paper for producing an art work in case of the use of a formed image as a printing manuscript. The length of the lengthwise direction of a developer bearing member provided in at least one developing device among the developing devices provided in the image forming apparatus is longer than those of the developer bearing members of the other developing devices.