A developing roll has a metal core, an elastic layer, and a surface layer. A value X is 65.6 N/mm.sup.3 or more and a value Y is 229 ?m or more. The value X is P.sub.1/(D.sub.1?A)?P.sub.2/(D.sub.2?A). P.sub.1 is the load to displace the roll 100 ?m when a metal probe is pressed against the roll. D.sub.1 is the displacement of the roll caused by the probe under the load P.sub.1. A is the area of the probe. P.sub.2 is the load to displace a material roll by 100 ?m when the probe presses against the material roll with the core and the elastic layer and without the surface layer. D.sub.2 is the displacement of the material roll caused by the probe under the load P.sub.2. The value Y is the displacement of the roll when the probe pierces the surface layer.

A developing device includes a developing container, a developing roller, a supplying roller, a first magnet including a first magnetic pole, a second magnet including second to fifth magnetic poles, and a regulating member. A maximum magnetic flux density of the second magnetic pole is larger in absolute value than a maximum magnetic flux density of the third magnetic pole in a normal direction to the supplying roller, and a maximum magnetic flux density of the third magnetic pole is larger in absolute value than a maximum magnetic flux density of the fourth magnetic pole in the normal direction. With respect to a rotational direction of the supplying roller, an angle between maximum magnetic flux density positions of the second and third magnetic poles is smaller than an angle between maximum magnetic flux density positions of the third and fourth magnetic poles.

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.

An image forming apparatus includes a developer carrying body to transfer developer to a photosensitive body. The developer carrying body has an outer circumference and grooves spaced apart along the outer circumference. The grooves occupy 27% or more of the outer circumference. The developing carrying body is rotatable in a rotational direction that imparts the developing carrying body with a direction of movement that is opposite to a direction of movement of the photosensitive body, at a position between the developer carrying body and the photosensitive body.

A developing device includes a developing container, a developing sleeve, a magnet and grooves provided at a surface of the sleeve and formed along a direction crossing a circumferential direction of the sleeve. In a cross-section, each of the grooves is formed by a flat bottom portion contacting a carrier particle and a pair of side surface portions provided in both sides of the flat bottom portion with respect to the circumferential direction of the sleeve and satisfies the following relationship:
r<w<2r,
2r<L, and
r/2s<2r. In the above, r is a volume-average particle size of the carrier particles, w is a length of the flat bottom portion, L is a width between the side surface portions at the surface of the sleeve, and s is a depth of each of the grooves.

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.

An image forming apparatus includes: a photosensitive member; a scan unit configured to scan the photosensitive member with light based on image data, and form a latent image on the photosensitive member; a developing unit configured to form an image on the photosensitive member by attaching toner to the latent image formed on the photosensitive member; and a correction unit configured to correct an exposure amount of the photosensitive member such that a density change of the image in a main scanning direction due to a configuration of the scan unit and a density of the image to be formed is reduced.

A developing device includes a developing sleeve configured to carry and convey developer containing non-magnetic toner and magnetic carrier and having a plurality of concave parts on a surface thereof. The concave parts are periodically arranged in each of a rotation direction and a width direction of the developing sleeve, and each have a shape that can house a circular shape having a diameter equal to an average particle diameter of the carrier carried on the developing sleeve, in a planar view. A distance between the concave parts is smaller than the average particle diameter.

In some examples, a developing device includes a developing container including an opening and to store a developer, a developing sleeve installed in the developing container and partially exposed to an outside of the developing container through the opening, a regulation member upstream of the opening in a rotation direction of the developing sleeve and to regulate an amount of the developer adhered to the developing sleeve and supplied to the opening, and a magnetic member inside the developing sleeve. The magnetic member includes a main pole facing the opening, a regulation pole facing the regulation member, and a catch pole upstream of the regulation pole in the rotation direction of the developing sleeve. The magnetic member is to cause adhesion of the developer in the developing container to the developing sleeve. At least one of lengths of the catch pole or the regulation pole and diameters of both end portions of the catch pole or the regulation pole are less than a length and a diameter, respectively, of the main pole.

A developing apparatus includes a developing container accommodating a developer, a developing sleeve having a plurality of magnetic poles arranged in a circumferential direction, and a regulating member configured to regulate a layer thickness of the developer carried on the developing sleeve. The magnetic poles include a regulation pole disposed opposed to the regulating member such that a maximum value position at which a magnetic flux density in a normal line direction of the developing sleeve is a maximum is not less than 3? away in a circumferential direction of the developing sleeve from a half peak center portion position which is a center portion position of a half-peak width of the magnetic flux density. The regulating member is disposed downstream of the half peak center portion position and upstream of the maximum value position with respect to a rotational direction of the developing sleeve.