An image forming apparatus (1, 1'), comprising: multiple image forming units (20Y, 20C, 20M) 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 (20Y, 20C, 20M) 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 (20K, 20K', 20K") to form a black image, the black image forming unit (20K, 20K', 20K") being disposed separately from the multiple image forming units (20Y, 20C, 20M), the black image forming unit (20K, 20K', 20K") including a black image carrier to carry the black image on a surface thereof; and a black image developing unit (4K, 4K') to develop the black image with black toner; a second transfer member disposed facing the black image carrier of the black image forming unit (20K, 20K', 20K") to transfer the black image from the black image forming unit (20K, 20K', 20K") onto a recording medium; a first cleaning unit disposed facing the black image carrier to clean the surface of the black image carrier by removing black toner from the surface of the black image carrier; wherein the first cleaning unit is configured to collect the black toner removed from the surface of the black image carrier; a second cleaning unit disposed facing the second transfer member to clean the surface of the second transfer member;, characterized by a residual toner conveyance path configured to return the black toner removed from the surface of the black image carrier to the black image developing unit (4K, 4K'); a residual toner collection path formed between the second cleaning unit and a developer agitation chamber of the black image developing unit (4K, 4K'); a residual toner collection unit including a transfer member toner collection screw that can rotate in a forward direction and a backward direction to convey residual toner collected from the second transfer member to the residual toner collection path when it rotates in the backward direction; and a waste toner path and a waste toner tank, wherein the waste toner path extends between the waste toner tank and the residual toner collection unit, and wherein the residual toner is conveyed to the waste toner path when the transfer member toner collection screw rotates in the forward direction. multiple image forming units (20Y, 20C, 20M) 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 (20Y, 20C, 20M) 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 (20K, 20K', 20K") to form a black image, the black image forming unit (20K, 20K', 20K") being disposed separately from the multiple image forming units (20Y, 20C, 20M), the black image forming unit (20K, 20K', 20K") including a black image carrier to carry the black image on a surface thereof; and a black image developing unit (4K, 4K') to develop the black image with black toner; a second transfer member disposed facing the black image carrier of the black image forming unit (20K, 20K', 20K") to transfer the black image from the black image forming unit (20K, 20K', 20K") onto a recording medium; a first cleaning unit disposed facing the black image carrier to clean the surface of the black image carrier by removing black toner from the surface of the black image carrier; wherein the first cleaning unit is configured to collect the black toner removed from the surface of the black image carrier; a second cleaning unit disposed facing the second transfer member to clean the surface of the second transfer member;, characterized by a residual toner conveyance path configured to return the black toner removed from the surface of the black image carrier to the black image developing unit (4K, 4K'); a residual toner collection path formed between the second cleaning unit and a developer agitation chamber of the black image developing unit (4K, 4K'); a residual toner collection unit including a transfer member toner collection screw that can rotate in a forward direction and a backward direction to convey residual toner collected from the second transfer member to the residual toner collection path when it rotates in the backward direction; and a waste toner path and a waste toner tank, wherein the waste toner path extends between the waste toner tank and the residual toner collection unit, and wherein the residual toner is conveyed to the waste toner path when the transfer member toner collection screw rotates in the forward direction.