Patent ID: 7664440

Claim:
A developing device comprising: a developing roller having a sleeve and a magnet roller, for bearing and conveying a two-component developer composed of a toner and a carrier, the sleeve being rotatably disposed facing a photoreceptor where an electrostatic latent image is formed, the magnet roller being fixedly disposed inside the sleeve to form a plurality of magnetic poles; and a layer-thickness regulating member disposed facing the developing roller, for regulating a layer-thickness of the two-component developer conveyed by the developing roller, wherein the magnet roller has a main pole for forming a magnetic pole in a developing region for feeding the toner to the photoreceptor, a regulating pole arranged upstream of the magnetic pole formed by the main pole in a rotation direction of the sleeve and so positioned as to be closest to the layer-thickness regulating member, and a pumping pole disposed for pumping the two-component developer upwardly in a vertical direction, wherein an angle α is in a range of no less than 45 degrees nor more than 57 degrees, which is formed between a plane comprising a central line of a magnetic pole formed by the regulating pole and a rotating central axis of the sleeve and a plane comprising a central line of a magnetic pole formed by the pumping pole and the rotating central axis of the sleeve, and wherein an absolute value of a maximum value of strength of a magnetic pole formed by the main pole is in a range of no less than 120 mT nor more than 140 mT.