A developing device includes a first developing roller, a second developing roller, a first end portion configured to restrict the amount of developer on the second developing roller, a restriction member, and a collecting roller configured to collect developer on the first developing roller. The second end portion is located at a position where magnetic force interference with a magnetic force generated by the second developing roller and the collecting roller is not caused.

At an end, in a longitudinal direction, of an opening in a container containing a magnetic developer, an overlap portion is provided in which a developer bearing member, a regulating member, a sealing member, and the container are arranged so as to sequentially contact one another in a direction orthogonal to a rotation axis direction. A magnetic field generating member provided inside the developer bearing member has a first area where a value of a magnetic flux density is a predetermined value in the rotation axis direction and a second area including a local minimum portion in which the value is a minimum value, within a range from an end of the second area connected to the first area to an outer end of the overlap portion in the rotation axis direction.

An opposing surface of a partition opposing a first conveyance screw includes an arc-shaped guide portion for guiding conveyance of developer at least on an upstream side in a first conveyance direction of the first conveyance screw. The guide portion is extended from a bottom portion of a first chamber opposing the first conveyance screw and formed along an outer periphery of the first conveyance screw. As seen in a cross section orthogonal to a rotation axis of the first conveyance screw, the opposing surface of the partition within a predetermined area includes the guide portion over an angle of 30% or more of the predetermined area in a direction of rotation of the first conveyance screw.

A developing device includes a developer bearer, a developer regulator disposed opposite the developer bearer across a first gap, and an opposing member having an opposing face disposed opposing the developer bearer across a second gap wider than the first gap. The opposing face is disposed adjacent to and upstream from the developer regulator in a direction of rotation of the developer bearer. The opposing face is inclined relative to an orthogonal plane direction orthogonal to a side face of the developer regulator. The opposing face is inclined to progressively reduce a distance from the developer bearer to the opposing face in a direction of rotation of the developer bearer. A difference between the second gap and the first gap is not greater than 1.75 times as large as the first gap.

According to one embodiment, the developing device includes a developing case containing toner, a mixer configured to diffuse the toner in the developing case, and a developing roller configured to develop a latent image formed on an image carrier. The developing case includes a circulation path through which air containing the toner flows. The developing roller is partially exposed from the developing case. The developing roller includes a sleeve rotating along with the movement of the image carrier and a plurality of magnetic pole portions disposed inside the sleeve. The developing roller holds the toner on the sleeve and supplies the toner to the image carrier to develop the latent image. The developing device further includes a magnet disposed apart from the developing roller. The magnet faces one of the magnetic pole portions across the sleeve.

A developing apparatus including: a first chamber including a first conveyance member conveying developer in a first direction; a second chamber including a second conveyance member having a conveyance portion conveying the developer in a second direction opposite to the first direction and a return conveyance portion provided downstream of the conveyance portion in the second direction to convey the developer in the first direction; a first partition wall provided between the first chamber and the second chamber to form a first communication portion and a second communication portion to form a circulation route; and a bearing member configured to rotatably support the second conveyance member and including: a discharge port provided downstream of the return conveyance portion; and a second partition wall extending from the bearing member in the first direction to cover a portion of the return conveyance portion confronting the first communication portion.

A developing device includes a developer container to contain developer including toner and magnetic carrier, the developer container; a developer bearer to carry, by rotation, the developer to a developing range facing a latent image bearer; a communication opening in a wall defining the developer container; a toner conveyance passage connected to the communication opening; and a cylindrical magnet having a magnetic pole arrangement parallel to an axis of the cylindrical magnet. The cylindrical magnet is disposed to enclose a space overlapping with the communication opening on a cross section perpendicular to the axis of the cylindrical magnet.

A developing device includes a developer container to contain developer including toner and magnetic carrier, the developer container; a developer bearer to carry, by rotation, the developer to a developing range facing a latent image bearer; a communication opening in a wall defining the developer container; a toner conveyance passage connected to the communication opening; and a cylindrical magnet having a magnetic pole arrangement parallel to an axis of the cylindrical magnet. The cylindrical magnet is disposed to enclose a space overlapping with the communication opening on a cross section perpendicular to the axis of the cylindrical magnet.

A development device including: a developer bearing; a regulation portion; a magnetic field generation member that is provided inside of the developer bearing member, the magnetic field generation member having: a development pole; a first magnetic pole; and a second magnetic pole; wherein the magnetic field generation member has a region satisfying |(Br(θa)−Br(θc))/10|<0.3, wherein Br(θa) is a magnetic flux density in a normal direction relative to the surface of the developer bearing member on a position shifted by −5° from a point nearest to the regulation portion on the developer bearing member around a center of the developer bearing member, and Br(θc) is the magnetic flux density around the developer bearing member on a position shifted by +5° from the point nearest to the regulation portion on the developer bearing member.

An image forming apparatus includes an image bearing member, an exposure device configured to expose the image bearing member to form an electrostatic latent image thereon, and a developing device including a rotatable developing member configured to carry and feed a developer containing toner and a carrier to develop the electrostatic latent image formed on the image bearing member, and a magnet provided non-rotatably and stationarily inside the rotatable developing member including a developing magnetic pole, wherein magnetic chains formed by the carrier, on the rotatable developing member, magnetized by the magnet contact the electrostatic latent image formed on the image bearing member in a developing region of the rotatable developing member, wherein a maximum peak position where a magnetic flux density of the developing magnetic pole is maximum with respect to a normal direction of the rotatable developing member exists within a range of the developing region with respect to a rotational direction of the rotatable developing member, and wherein a ratio of an 80%-value-width which is a width of a portion where the magnetic flux density of the developing magnetic pole with respect to the normal direction of the rotatable developing member is 80% of the maximum of the magnetic flux density of the developing magnetic pole with respect to the normal direction of the rotatable developing member to a half peak width which is a width of a portion where the magnetic flux density of the developing magnetic pole with respect to the normal direction of the rotatable developing member is half of the maximum of the magnetic flux density of the developing magnetic pole with respect to the normal direction of the rotatable developing member is 0.65 or more.