Patent ID: 8588663

Claim:
A developing device comprising: a developer holding body comprising: a hollow development rotary body which is opposed to an image holding body capable of holding a toner image and has a smooth surface whose surface roughness is lower than or equal to 5 μm in terms of maximum height; and a magnet member which is fixedly housed in the development rotary body and in which a plurality of magnetic poles are arranged alongside its periphery, the developer holding body operating in such a manner that developer containing toner and carrier is held on the development rotary body by magnetic force produced by the magnetic poles of the magnet member as the development rotary body is rotated, wherein the magnetic member of the developer holding body comprises a layer regulating magnetic pole which produces a magnetic flux density of 30 to 60 mT in a region where a layer regulating rotary body and the development rotary body are closest to each other; said layer regulating rotary body which is opposed to the development rotary body with a non-contact gap formed between them so as to regulate the thickness of a developer layer held on the developer holding body, a first portion, facing the development rotary body, of the layer regulating rotary body being able to move in the same direction as a second portion of the development rotary body, the second portion facing the first portion; the layer regulating rotary body rotating in a direction opposite to a direction of rotation of the development rotary body; and a development driving device for rotationally driving the development rotary body of the developer holding body and the layer regulating rotary body and variably adjusting the circumferential speed of the layer regulating rotary body according to an increase or decrease in the thickness, to be regulated, of a developer layer held on the developer holding body, during a development operation.