An absolute value of a first maximum value is smaller than an absolute value of the second maximum value. With respect to a rotational direction of a rotatable developing member, an angle from a second maximum position to a position where a magnetic flux density of a regulating pole in a normal relative to an outer peripheral surface of the rotatable developing member is a half value of the second maximum value on a side downstream of the second maximum position is smaller than an angle from a position where the magnetic flux density of the regulating pole in the normal direction relative to the outer peripheral surface of the rotatable developing member is a half value of the first maximum value on a side upstream of the first maximum position to the first maximum value.

A developing device includes a developing container storing a two-component developer containing a magnetic carrier and a toner, a developer carrying member carrying the developer on its outer circumferential surface, and a regulation member arranged to be opposed at a prescribed distance to the developer carrying member. The developer carrying member includes a developing sleeve on which a magnetic brush is formed, and a magnet secured in the developing sleeve and having a plurality of magnetic poles including a regulation pole opposed to the regulation member and a downstream-side magnetic pole arranged downstream of the regulation pole with respect to the rotation direction of the developing sleeve. The magnet is such that the vertical magnetic force gradient [mT/° ] has a local minimum value near a position at which the vertical magnetic force is 0 [mT] between the downstream-side surface of the regulation member and the downstream-side magnetic pole.

A magnet roller employs a magnetic pole pattern in which a first magnetic pole arranged substantially opposing a regulating blade in an upstream side of a rotation direction of a developing sleeve and a second magnetic pole next to the first magnetic pole in the upstream side have the same polarity, an opposing member having surface roughness higher than at least a particle diameter of carrier is arranged opposing the magnet roller at a position where magnetic force between the first magnetic pole and the second magnetic pole next to the first magnetic pole in the upstream side is almost zero, and an apex of a partition wall provided between a developer bearing member and a developer conveying member provided in a first chamber is positioned below a region where magnetic force formed by the magnet roller is almost zero.

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 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.

A change of a magnetic flux density distribution adjacent to a regulating blade 9 opposed to a developer regulation pole is suppressed at a low cost, while suppressing influence to design latitude of magnetic poles. A position on the outer peripheral surface of the developing sleeve where the magnetic flux density in the normal line direction of the outer peripheral surface of the developing sleeve is a maximum value position. The position on the outer peripheral surface of the developing sleeve 8 corresponding to a center portion position of the half peak range of the magnetic flux density distribution of the developer regulation pole is called half peak center portion. The developer regulation pole is formed such that the maximum value position is deviated not less than 3° in the circumferential direction of the developing sleeve from the half peak center portion position, and the position when the regulating blade 9 opposite is the developing sleeve is in a side of the maximum value position in which the half peak center portion position exists.

A developing device includes a housing, a developing roller, a developer stirring member, and a layer thickness regulating member. The developing roller includes a stationary magnet and a sleeve. The stationary magnet includes a first magnetic pole having a specific polarity, and a second magnetic pole lying downstream of the first magnetic pole and having the same polarity as the first magnetic pole. In an entire inter-pole region between the first magnetic pole and the second magnetic pole, the stationary magnet produces a magnetic force including a horizontal component that keeps the specific polarity and has a value greater than zero (mT). The inter-pole region includes a flat area where a horizontal magnetic force component having a minimum absolute value exits and the horizontal magnetic force component changes within a range of 0.5 (mT) or less, the flat area extending over a range of 10 degrees or more.

A developer roll according to one example embodiment includes a core including at least one permanent magnet forming a magnetized portion of the core. A cylindrical sleeve positioned around the core is rotatable relative to the core about an axis of rotation in an operative rotational direction. A release pole of the permanent magnet is positioned to magnetically attract developer mix to an outer circumferential surface of the sleeve to transport developer mix on the surface of the sleeve in the operative rotational direction when the sleeve rotates relative to the core to a release point where a magnetic field of the permanent magnet is insufficient to retain developer mix against the surface of the sleeve. An axial length of the magnetized portion of the core decreases at both axial ends of the core as the magnetized portion of the core approaches the release point in the operative rotational direction.

Provided is a developer carrying member that can stably form a high-quality electrophotographic image. The developer carrying member includes an electroconductive support and a surface layer in the stated order, wherein the surface layer contains a binder resin and electroconductive particles, and a content of the electroconductive particles in a region from a surface of the surface layer opposite to an outer surface thereof on a side facing the electroconductive support to a depth of 150 nm is 1% or more and 25% or less, and wherein the surface layer has a volume resistivity of 1.0×10.sup.−2 Ω.Math.cm or more and 1.0×10.sup.2Ω.Math.cm or less.