A developing device has a housing, a developer carrying member, a regulating blade, and a magnetic member. The regulating blade forms a regulating portion regulating the thickness of toner carried on the developer carrying member. The magnetic member is arranged inside the developer carrying member and has a plurality of magnetic poles including a regulating pole arranged at a position where the developer carrying member and the regulating blade are close together. The regulating pole is movable to a first position facing the regulating portion and to a second position rotated to the upstream side from the first position in the rotation direction of the developer carrying member during image formation. The developing device is operable in the developer removing mode in which, when no image is formed, the regulating pole is moved from the first position to the second position and is then returned to the first position.

A developing device includes a housing, a developer carrier, a regulating blade forming a regulating portion for regulating the layer thickness of developer on the developer carrier, a magnetic member arranged inside the developer carrier and having a plurality of magnetic poles including S and N poles, and a blade magnet inducing a magnetic pole at the tip end of the regulating blade. The magnetic member is movable between a first position where a magnetic pole having the same polarity as that of the facing magnetic pole of the blade magnet facing the developer carrier is arranged at a regulating portion and a second position where a magnetic pole having a different polarity is arranged at the regulating portion. The developing device can perform a first developer eliminating mode where the magnetic member is moved to a second position and the developer carrier is rotated forward during non-image forming period.

A developing device has a housing, a developer carrying member, a regulating blade, and a magnetic member. The regulating blade forms a regulating portion regulating the thickness of toner carried on the developer carrying member. The magnetic member is arranged inside the developer carrying member and has a plurality of magnetic poles including a regulating pole arranged at a position where the developer carrying member and the regulating blade are close together. The regulating pole is movable to a first position facing the regulating portion and to a second position rotated to the upstream side from the first position in the rotation direction of the developer carrying member during image formation. The developing device is operable in the developer removing mode in which, when no image is formed, the regulating pole is moved from the first position to the second position and is then returned to the first position.

An image forming apparatus includes an image forming portion including a photosensitive member and a developing portion, a sheet accommodating portion, a sheet feeding portion, and a first frame. The first frame includes an upper space supporting the image forming portion, and a lower space under the upper space. A second frame is mountable to a lower portion of said first frame. The accommodating portion and the feeding portion are replaceable with a supply container containing toner to be supplied to a developing portion of the image forming portion, in which the second frame supports the accommodating portion and the feeding portion.

A developing device includes a rotatable developing sleeve for carrying a developer including toner and a magnetic carrier and for developing an electrostatic latent image, formed on an image bearing member, in a developing region where the developer contacts the image bearing member; and a magnetic field generating portion provided inside the developing sleeve and having a developing pole provided at a position opposing the image bearing member in order to form the developing region, wherein a ratio of an 80%-value-width of magnetic flux density of the developing pole with respect to a normal direction of the developing sleeve to a half peak width of the magnetic flux density of the developing magnetic pole with respect to the normal direction is 0.65 or more, and with respect to a rotational direction of the developing sleeve, a magnetic force of the developing pole in the normal direction of the developing sleeve in each of neighborhoods of both end portions of the developing region is larger than a magnetic force of the developing pole at a central portion of the developing region.

A magnetic one-component developer includes magnetic toner particles containing a binder resin and a magnetic powder, and silica particles having a compression and aggregation degree of 60% or more and 95% or less and a particle compression ratio of 0.20 or more and 0.40 or less.

Magnetic one-component toner has toner particles including: a toner base particle containing at least a binder resin and a magnetic powder; and an external additive attached to the surface of the toner base particle. The toner base particle contains a nigrosine dye. The external additive contains strontium titanate particles of which the surface is hydrophobically treated. The amount of nitrogen element in toner particles is 0.5 mass % or more but 5 mass % or less. The Abs value representing the amount of nigrosine dye that dissolves when toner particles are immersed in methanol as expressed in terms of light absorbance is 0.2 or more but 2.0 or less. The volume resistivity of strontium titanate particles is 1.0 E+7 [.Math.cm] or more but 1.0 E+10 [.Math.cm] or less.

A magnetic one-component toner includes toner particles each including a toner base particle and an external additive attached to a surface of the toner base particle. The external additive includes conductive particles with a specific resistance of 1.0E+4 [.Math.cm] or lower, resin particles with a number average primary particle sizes of 50 nm or more but 100 nm or less, and silica particles. The resin particles are formed by using an anion surfactant and formed from a vinyl resin having a repeating unit represented by general formula (1) below, a repeating unit represented by general formula (2) below, and a repeating unit derived from a sulfo group-containing vinyl compound. A content ratio of the repeating unit derived from the sulfo group-containing vinyl compound in the vinyl resin is 2.0 mol % or more but 5.0 mol % or less relative to all repeating units in the vinyl resin.

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