PURPOSE: To uniformize a developer thin layer formed on a carrier by allowing a developer to pass a gap between the periphery of a developer carrier and a porous thin plate.

CONSTITUTION: In this developing device 10, the developer housed in a housing is rubbed by a supplying roller 12 to be electrified to a negative polarity, and carried into the gap between the periphery of a roller 11 and a mesh member 14 by the rotation of a roller 12 and a bias potential between the roller 12 and the developing roller 11. Then, the developer is almost uniformly triboelectrified over the whole area in the axial direction of the roller 11, while being rubbed on the periphery of the roller 11 and the mesh 14, and the developer thin layer is formed and carried to a region abutted on a photosensitive drum 20.