A color image forming apparatus in which a charging, imagewise exposing and developing operations are repeated onto an image forming drum to register different colored toner images thereon and thereby to transfer simultaneously the toner images onto a recording sheet, includes four imagewise exposing units which are disposed inside the image forming drum and are fixed in a main body of the image forming apparatus. Two each of the exposing units and the developing units are disposed respectively on both sides with predetermined angles with respect to a vertical line passing through the center of the image forming drum. The apparatus further includes a transferring device and a cleaning device are disposed respectively with predetermined angles on different one side of the vertical line below a horizontal line intersecting with the center of the image forming drum.