A color image forming apparatus is provided, having a plurality of image forming units; a carriage for retaining and rotating the plurality of image forming units so as to move the image forming units between an image forming position and a waiting position; an intermediate transfer belt for successive transfer and superposition of toner images of various colors from a photosensitive drum of the image forming units located at the image forming position so as to form a color toner image; and a secondary transfer roller for transferring the color toner image on the intermediate transfer belt onto recording paper. The only rollers support the intermediate transfer belt are a driving roller, a following roller, a primary transfer roller and a backup roller, and the primary transfer roller and the backup roller are arranged adjacent to the driving roller.