Abstract: An image forming apparatus includes a photosensitive unit and a developing unit, at least one of which is arranged rotatable about a parallel support shaft. In a state that the both units are mounted on an apparatus main body, a developing roller gear (driven gear) of the developing unit is in mesh with a drive gear provided on the photosensitive unit. A drive force is transmitted from the drive gear to the developing roller gear. The developing roller gear and the drive gear are arranged such that a drive force acting on a pitch point has an extension line passing through a center of the parallel support shaft.

Abstract: A clamshell type image forming apparatus, in which a process cartridge included in an upper structure is supported pivotably to a fixed position and a dismounting position against the upper structure, a developing unit included in a lower structure is supported thereon pivotably to a position just opposing to an image holding medium and a position spaced therefrom, and a plate spring which urges the developing unit toward a position spaced from the image holding medium is disposed on the lower structure side, and a plate spring which urges the developing unit toward a position just opposing to the image holding medium is disposed on the upper structure side, thereby inconveniences produced by providing the process cartridge on the upper structure are solved, and by reducing a collision between the developing unit and the image holding medium due to the open-and-close operation of the upper structure, it is possible to prevent a damage of the process cartridge including the image holding medium.