In a developing apparatus, a distance along an outer peripheral surface of a rotatable developing member between a first and a second maximum peak positions is less than 18 [mm], the first and the second maximum peak positions respectively corresponding to maximum values of a magnetic flux density of a first and a second magnetic poles with respect to a normal direction of the rotatable developing member. A distance along the outer peripheral surface of the rotatable developing member in a width of a value obtained by adding 2 [mT] to a minimum value of the magnetic flux density with respect to the normal direction of the rotatable developing member is 5.5 [mm] or more, at a downstream side of the first maximum peak position and at an upstream side of the second maximum peak position with respect to a rotation direction of the rotatable developing member.

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 device includes a developer container, a developing roller, and a doctor member. The developer container contains a developer including a toner and a developer. The developing roller includes a developing sleeve bearing the developer, a magnet roller in the developing sleeve. The doctor member includes a regulating portion regulating an amount of the developer home on the developing sleeve to be a predetermined amount. The regulating portion is disposed with a first distance from the developing sleeve. The developing sleeve is disposed with a second distance from an image hearer, and when the developing sleeve bearing the predetermined amount of developer passes a vicinity of the image bearer, a value obtained by dividing the predetermined amount by the second distance is less than a threshold of occurrence of adherence of the developer to the developing sleeve.

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 roller includes: a magnet roller including a roll part with a magnetic pole; a cylindrical sleeve that houses the magnet roller; a first flange connected to one end of the sleeve; a second flange connected to another end of the sleeve; a conductive shaft connected to a side of the second flange of the magnet roller; a first bearing that supports the first flange so that the first flange rotates relative to the magnet roller; and second bearings that support the second flange so that the second flange rotates relative to the conductive shaft. The second bearings are conductive, and are disposed at different positions along an axial direction of the conductive shaft.

A powder supply device includes: a storage unit that stores a mixed agent including a functional material-containing powder and magnetic powder, the storage unit being provided with a discharge port through which a part of the stored mixed agent is discharged; a supply unit that holds the mixed agent and supplies the functional material-containing powder from the storage unit; and a magnetic body that covers at least a part of the discharge port and forms a nap of the mixed agent to prevent the mixed agent that is dispersed in air from flowing out through the discharge port.

A powder supply device includes: a storage unit that stores a mixed agent including a functional material-containing powder and magnetic powder, the storage unit being provided with a discharge port through which a part of the stored mixed agent is discharged; a supply unit that holds the mixed agent and supplies the functional material-containing powder from the storage unit; and a magnetic body that covers at least a part of the discharge port and forms a nap of the mixed agent to prevent the mixed agent that is dispersed in air from flowing out through the discharge port.

A developing device includes a developer container, a developing roller, and a doctor member. The developer container contains a developer including a toner and a developer. The developing roller includes a developing sleeve bearing the developer, a magnet roller in the developing sleeve. The doctor member includes a regulating portion regulating an amount of the developer home on the developing sleeve to be a predetermined amount. The regulating portion is disposed with a first distance from the developing sleeve. The developing sleeve is disposed with a second distance from an image hearer, and when the developing sleeve bearing the predetermined amount of developer passes a vicinity of the image bearer, a value obtained by dividing the predetermined amount by the second distance is less than a threshold of occurrence of adherence of the developer to the developing sleeve.

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 fourth 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 by 10 degrees or more.

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.