Abstract: An image forming apparatus usable with a process cartridge detachably mountable thereto. The process cartridge includes a main cartridge containing a photosensitive member and process means as a unit. A subordinate process cartridge is detachably mountable to the main cartridge. The subordinate cartridge includes at least a developing device which is different from the developing device contained in the main cartridge so that a multi-color image can be formed if desired. The photosensitive member is used both for the main process cartridge and the subordinate cartridge.

Abstract: An image forming apparatus includes a first developing device for forming a first toner image and a second developing device for forming a second toner image including a developer carrying member spaced apart from the image bearing member by a distance and a device for applying a developing bias voltage to form an electric field having a maximum voltage Vmax and a minimum voltage Vmin, such that when the first developer is positively charged,.vertline.Vmin-V.sub.T .vertline./d.ltoreq.2.25, or when the first developer is negatively charged,.vertline.Vmax-V.sub.T .vertline./d.ltoreq.2.25,where V.sub.T (V) is a potential of a first toner image immediately before formation of the second toner image after the first latent image is subjected to the charger, the potential of the first toner image being a surface potential of the first toner image under existence of the first latent image.

Abstract: An image forming apparatus includes a movable image bearing member; a device for forming a first latent image and a second latent image; a first developing device for developing the first latent image using a first developer containing magnetic particles and toner particles to form a first developed image; a second developing device, disposed downstream of the first developing means with respect to movement direction of the image bearing member, for developing the second latent image on the image bearing member bearing the first developed image and the second latent image, using a second developer which is different from the first developer, the second developing device including a developer containing portion and developer carrying sleeve for carrying from the developer containing portion the second developer to a developing zone where the developer carrying sleeve is opposed to the image bearing member; and a magnetic field generating pole, in the second developing device, for providing an attracting surfac