Developing device and image forming device

1. A developing device comprising:

a developer housing chamber in which developer is housed;

a developer holding member holding developer by magnetic force;

a partitioning wall that is a portion of a separating wall of the developer housing chamber and is provided between the developer housing chamber and the developer holding member, the partitioning wall having an overlapping region that, in a transparent plan view, is positioned upward of the developer holding member and overlaps the developer holding member in an up/down direction; and

an opening portion formed in the overlapping region of the partitioning wall.

2. The developing device of claim 1 , wherein the developer holding member has:

magnetic field generating member provided with a developing magnetic pole portion that faces an image holding body and holds developer, a conveying magnetic pole portion that is a different polarity than the developing magnetic pole portion and draws developer of the developing magnetic pole portion, and a peeling magnetic pole portion that is a same polarity as the developing magnetic pole portion and peels-off developer that is drawn to the conveying magnetic pole portion; and

a rotating body that is tubular and is provided rotatably at a periphery of the magnetic field generating member, and at whose outer peripheral surface developer is held on or is peeled-off from, and

the opening portion is positioned so as to oppose a region from the conveying magnetic pole portion to the peeling magnetic pole portion.

3. The developing device of claim 2 , wherein the opening portion is provided at a region where magnetic flux density of the peeling magnetic pole portion is highest.

4. The developing device of claim 1 , wherein an internal region of the opening portion is positioned partially within the overlapping region.

5. The developing device of claim 1 , wherein

the developer holding member is provided at a developing chamber, and

a wall portion of the partitioning wall, which wall portion is at a lower side of the opening portion, is bent toward a direction of gravity more than an angle of inclination of a wall portion that is at an upper side of the opening portion.

6. The developing device of claim 5 , wherein the bent wall portion of the partitioning wall, which wall portion is at the lower side of the opening portion, is substantially inverted-V-shaped.

7. The developing device of claim 1 , wherein

the developer holding member is provided at a developing chamber, and

a wall portion of the partitioning wall, which wall portion is at a lower side of the opening portion, is rectilinear.

8. The developing device of claim 1 , wherein a side wall of the developer housing chamber, which side wall opposes the partitioning wall, is bent toward an inner side of the developer housing chamber, and a reduced diameter portion where a sectional surface area of the developer housing chamber is reduced is formed.

9. The developing device of claim 1 , wherein a lower edge portion of the opening portion is disposed further upward than a rotational center of the developer holding member.

10. The developing device of claim 1 , wherein the opening portion is sealed by a sealing member that can be removed.

11. An image forming device comprising a plurality of image forming units, each of which has the developing device of claim 1 and makes a latent image visible by the developing device, wherein the image forming units that are adjacent overlap in an up/down direction at positions of the developer housing chambers.