Patent ID: 8090276

Claim:
A developing device, comprising: a developer container that contains a two-component developer including a carrier and a toner attached to the carrier through a frictional electrification; a developing roller that carries the two-component developer from the developer container to an image carrier; a first screw carrying a developer; and a second screw carrying the developer in a direction opposite to a direction in which the first screw carries the developer, wherein the first screw is used to supply the developer to the developing roller, whilst the second screw is used for stirring a new toner and the carrier for a friction charge on the toner, the first screw and the second screw circularly convey the two-component developer while stirring the two-component developer to supply the two-component developer to the developing roller, a rotation speed of the second screw and a rotation speed of the developing roller can be controlled independently, and a ratio of the rotation speed between the second screw and the developing roller is variable.