Color image forming apparatus

A color image forming apparatus comprising:

• a plurality of image forming units corresponding to various colors, each of said image forming units comprising a developing device;
• a unit retaining member for retaining said image forming units and moving said image forming units between an image forming position and a waiting position;
• a photosensitive drum having a surface on which various color toner images developed by said developing device are formed;
• an intermediate transfer unit comprising an intermediate transfer belt for successive transfer and superposition of toner images of various colors from said photosensitive drum so as to form a color toner image on a surface of said intermediate transfer belt;
• and
• a secondary transfer device for transferring the color toner image on said intermediate transfer belt onto a transfer material,
• wherein said intermediate transfer unit comprises four rollers:
• a driving roller for supporting said intermediate transfer belt and driving said intermediate transfer belt;
• a following roller for supporting said intermediate transfer belt and following said intermediate transfer belt;
• a primary transfer roller for supporting said intermediate transfer belt;
• and
• a backup roller for supporting said intermediate transfer belt and arranged in opposition to said secondary transfer device,
• said primary transfer roller is arranged between said following roller and said driving roller with respect to a rotation direction of said intermediate transfer belt, and
• said backup roller is arranged between said following roller and said driving roller with respect to the rotation direction of said intermediate transfer belt, on a side that is different from a side of said primary transfer roller,
• the only rollers supporting said intermediate transfer belt are said driving roller, said following roller, said primary transfer roller and said backup roller, and said primary transfer roller and said backup roller are arranged adjacent to said driving roller.