Developing device and image forming apparatus

1. A developing device comprising:

an agitating transport device that has a transport path and that transports developer including a magnetic carrier while agitating the developer;

a density detecting device that detects density of the developer in the transport path of the agitating transport device; and

an attracting device that is disposed on the agitating transport device and that has magnetic poles of one and another polarities exposed to the transport path facing the density detecting device so as to attract the developer by a magnetic force,

wherein the agitating transport device includes a flat plate-shaped retaining device that transports to a position facing the density detecting device the developer in a circumferential direction of the agitating transport device so as to cause the developer to be retained, and

wherein the attracting device is held by the retaining device.

2. The developing device according to claim 1 ,

wherein the attracting device has, in an axial direction of the agitating transport device, one and another end portions positioned inside the retaining device.

3. The developing device according to claim 1 ,

wherein the retaining device has a central portion in an axial direction of the agitating transport device and a recess formed at the central portion, and

wherein the magnetic poles of the one and the other polarities of the attracting device are exposed to the transport path in the recess of the retaining device.

4. The developing device according to claim 3 ,

wherein the retaining device is disposed such that, in the axial direction of the agitating transport device, a center of the density detecting device is positioned in the recess of the agitating transport device.

5. The developing device according to claim 4 ,

wherein the retaining device is disposed such that, in the axial direction of the agitating transport device, the center of the density detecting device is coincident with a center of the recess.

6. The developing device according to claim 1 ,

wherein the retaining device has an elastically deformable securing piece, and

wherein the attracting device is secured by the securing piece.

7. A developing device comprising:

an agitating transport device that has a transport path and that transports developer including a magnetic carrier while agitating the developer;

a density detecting device that detects density of the developer in the transport path of the agitating transport device; and

an attracting device that is disposed on the agitating transport device and that has magnetic poles of one and another polarities exposed to the transport path facing the density detecting device so as to attract the developer by a magnetic force,

wherein the agitating transport device includes a retaining device that has a projection at part of the retaining device,

wherein, in a radial direction of the agitating transport device, the projection projects further outward than the attracting device, and

wherein the attracting device is held by the projection of the retaining device.

8. The developing device according to claim 7 ,

wherein, in an axial direction of the agitating transport device, a length of the projection is smaller than a length of the attracting device.

9. A developing device comprising:

means for agitating and transporting that has a transport path and that transports developer including a magnetic carrier while agitating the developer;

means for detecting density that detects density of the developer in the transport path of the means for agitating and transporting; and

means for attracting that is provided in the means for agitating and transporting and that has magnetic poles of one and another polarities exposed to the transport path facing the means for detecting density so as to attract the developer by a magnetic force.