In an image forming apparatus, a moving member supports developing units and is movable between a mounted position and a pulled-out position. A drum supporting member integrally supports photosensitive drums. The drum supporting member is detachably supported by the moving member. An endless belt is disposed above the moving member when the moving member is disposed in the mounted position. The drum supporting member is configured so as to be detached upward from the moving member, while the moving member supports the developing units and the moving member is in the pulled-out position.