An image forming apparatus is provided to maintain a relatively high strength of a developer supply member and to minimize a change of density in a horizontal direction of an image. A developing unit(120) includes a unit casing(121) that forms a developing chamber(K) and rotors(122-126) rotatably provided in the developing chamber. A developer supply unit(110) stores a developer therein and includes a plurality of developer outlets(114) formed to overlap with each other or to be in contact with each other along a rotation direction of the rotors. The developer supply unit includes a developer storage tank and a hollow developer supply member(113) having a developer inlet through which the developer of the developer storage tank is introduced and the plurality of developer outlets formed on an outer surface thereof, and accommodated in the developing chamber.
