Patent ID: 7715762

Claim:
A developing apparatus comprising: a developer containing tank, which contains developer containing toner and includes an opening facing an image holder, and in which a developer holder is rotatably provided at a position facing the opening; first and second agitating and carrying members provided parallel to the developer holder in the developer containing tank, the first and second agitating and carrying members agitating and carrying the developer in directions opposite to each other; a partition member, provided between the first and the second agitating and carrying members, which partitions an inside of the developer containing tank so as to form (i) a first carrying path where the first agitating and carrying member carries the developer in a longitudinal direction of the first carrying path and (ii) a second carrying path where the second agitating and carrying member carries the developer in a longitudinal direction of the second carrying path, the developer flowing in directions opposite to each other in the longitudinal directions of the first and second carrying paths; and toner concentration detecting means provided in the first carrying path on a downstream side with respect to a center section of the first agitating and carrying member in the flow of the developer carried in the longitudinal direction of the first carrying path, the first and second carrying paths communicating each other through communicating paths provided at end sections of the first and second carrying paths, and circulating the developer between the first and second carrying paths, the first agitating and carrying member having in its vicinity a toner supply opening, through which toner is supplied, on an upstream side in the flow of the developer carried by the first agitating and carrying member in the longitudinal direction of the first carrying path, the first agitating and carrying member being provided farther from the developer holder than the second agitating and carrying member, the partition member including a plurality of communicating openings, provided from a center section in a longitudinal direction to an end section on a side where the toner supply opening is provided, which communicating openings return the developer from the second carrying path to the first carrying path, the developer being returned from the second carrying path to the first carrying path, through the communicating path and the communicating openings, and the plurality of communicating openings becoming larger toward the end section of the partition member on a side where the toner supply opening is provided.