A color image forming apparatus having a plurality of developing units for containing different color toners to form a color image, a plurality of photo-receptor units including photo-receptors on which electrostatic latent images to be developed by said developing units are to be formed, and an intermediate transfer body unit including a tensionally provided belt with upper and lower surfaces to which toner images are transferred from said photo-receptors, an intermediate transfer body unit cartridge integrally holding said intermediate transfer body unit, the cartridge being detachably attached to the color image forming apparatus through the jamming-removal opening.