1. An image forming apparatus, comprising: multiple image forming units disposed adjacent to and horizontally aligned with each other to form respective single non-black color images; a first transfer member extending along and disposed in contact with the multiple image forming units to sequentially transfer and overlay the respective single non-black color images onto an extended surface thereof for forming a composite color image; a black image forming unit disposed separately from the multiple image forming units to form a black image, the black image forming unit including a black image carrier to carry the black image on a surface thereof; and a black image developing unit to develop the black image with black toner; a second transfer member disposed facing the black image carrier of the black image forming unit to transfer the black image from the black image forming unit onto a recording medium; a first cleaning unit disposed facing the black image carrier to clean the surface of the black image carrier; and a second cleaning unit disposed facing the second transfer member to clean the surface of the second transfer member, the black toner removed from the surface of the black image carrier being collected and returned to the black image developing unit.