PURPOSE: An image forming apparatus is provided to arrange the second image forming units with a middle transferring belt between the second image forming units which face each other, thereby reducing a size of a color image forming apparatus. CONSTITUTION: The first to fourth developers individually prepared according to each color are arranged in the first image forming units(141) at fixed intervals. The second image forming units(142) comprise one or more supplementary developer supplementing colors of the first image forming units. A printing image carrier(130) receives the printing images of the first and second image forming units.
