Patent ID: 8175502

Claim:
A developing device, comprising: a developing roller to bear developer, including magnetic carriers and toner, on a circumferential surface thereof, so as to develop a latent image formed on an image bearing member; and a developer supplying section to supply the developer onto the developing roller; wherein the developing roller is provided with: a developing sleeve that is made of a non-magnetic material; and a magnetic member that is installed into an inner space of the developing sleeve and provided with a plurality of fixed magnetic poles including at least a peeling magnetic pole; and wherein, when a reference position is defined as such a position that exhibits a maximum value of a magnetic flux density to be generated in a normal direction by the peeling magnetic pole, a magnetic-flux density flat region within which the magnetic flux density is kept at substantially a constant value being closely approximate to the maximum value of the magnetic flux density and the reference position is included, exists while fulfilling an Equation indicated as follow: Z≧ 7° where numeral Z indicates an angle of the developing roller in the magnetic-flux density flat region.