Patent ID: 7796920

Claim:
A developing unit to circulate a developer unidirectionally, comprising: a developer carrier provided at a position facing an image carrier; a magnetic field generator provided inside the developer carrier; a supply part housing a supply screw configured to supply a developer to the developer carrier along a rotation axis of the developer carrier; a collecting part provided under the supply part and housing a collecting screw; an agitation part provided at a side of the supply part and the collecting part and housing an agitation screw including an upstream part and a downstream part; a first opening penetrating the collecting part and the agitation part configured to transport the developer from a downstream part of the collecting screw to the upstream part of the agitation screw in a developer circulation; a second opening penetrating the agitation part and the supply part configured to transport the developer from the downstream part of the agitation screw to an upstream part of the supply screw; and a third opening penetrating the supply part and the collecting part configured to transport the developer from a downstream part of the supply screw to the downstream part of the collecting screw, wherein an unused developer is supplied via a supply port located above the third opening through which the developer is transported from the supply screw to the collecting screw, and wherein a height of a bottom surface of the downstream part of the agitation screw is higher than a height of a bottom surface of the supply screw such that the developer flows downward through the second opening.