PURPOSE: To set accurately relative positional relations between a developing device and a photosensitive body by providing a frame with a means which positions the developing device in each position.

CONSTITUTION: When a unit 13 is pulled out in the direction of an arrow (a) together with its frame 14 in case of the maintenance work such as replacement or the like of a photosensitive body 8, the unit 13 can be moved from a prescribed position of a copying machine body 1 to such position that movement of a developing device 9 is not hindered. When the developing device 9 is moved right in this state while being lifted, the developing device 9 is shifted to a distant position along the angular motion locus of a four-joint link mechanism 24. The developing device 9 is detached only by lifting because the device 9 is only placed on a supporting member 17 constituting a part of the four-joint link mechanism 24 through bosses 16 and 16, and a developer is replaced easily, and the photosensitive body 8 is replaced quickly because the developing device 9 is detached from the photosensitive body 8 in one touch.