The present invention relates to an image forming apparatus comprising a plurality of image forming units for forming images, the image forming units being detachably arranged in the image forming apparatus, and a plurality of developer supplying units arranged corresponding to each of the image forming units for supplying developing agents to the image forming units, the developer supplying units being detachably attached to the image forming apparatus. The image forming units and the developer supplying units are alternatively so disposed that one end in a longitudinal direction of the respective image forming units intersects with one end in a longitudinal direction of the respective developer supplying units.