An image forming apparatus includes an image forming portion including a photosensitive member and a developing portion configured to develop, with toner, an electrostatic latent image formed on the photosensitive member, the image forming portion being configured to form an image on the sheet, a first frame including an upper space supporting the image forming portion and a lower space under the upper space, an accommodating portion configured to accommodate the sheet, a feeding portion configured to feed the sheet accommodated in the accommodating portion, and a supply container configured to contain the toner to be supplied to the developing portion of the image forming portion. The accommodating portion and the feeding portion are provided in the lower space and, alternatively, the supply container is provided in the lower space together with a second frame which is mountable to a lower portion of the first frame.

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.

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.

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.

An image forming apparatus includes an image forming unit, a toner detection sensor, a storage unit, and a control unit. The image forming unit includes an image carrier, a charging device, an exposure device, and a developing device. The toner detection sensor detects toner in the developing device. The control unit predicts transition of the toner deterioration degree in the developing device using the toner consumption amount and the cumulative operating time stored in the storage unit, and a predetermined toner deterioration model. The control unit is capable of measuring the toner deterioration degree based on amplitude of an output value of the toner detection sensor, and corrects the toner deterioration model, if the measured value of the toner deterioration degree is apart from the predicted value of the toner deterioration degree by a predetermined value or more.

An image forming apparatus includes an image forming unit, a toner detection sensor, a storage unit, and a control unit. The image forming unit includes an image carrier, a charging device, an exposure device, and a developing device. The toner detection sensor detects toner in the developing device. The control unit predicts transition of the toner deterioration degree in the developing device using the toner consumption amount and the cumulative operating time stored in the storage unit, and a predetermined toner deterioration model. The control unit is capable of measuring the toner deterioration degree based on amplitude of an output value of the toner detection sensor, and corrects the toner deterioration model, if the measured value of the toner deterioration degree is apart from the predicted value of the toner deterioration degree by a predetermined value or more.

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.

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 to carry and feed a developer including toner and a carrier toward a developing region, and a magnetic field generating portion provided inside the developing sleeve and having a developing magnetic pole for forming the developing region. The developing magnetic pole is disposed opposite to a closest position of the image bearing member to the developing sleeve. A ratio of an 80%-value-width of magnetic flux density of the developing magnetic 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.

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.