A developing device includes a casing to contain developer, a developer bearer, an upper and lower developer conveyors to convey the developer to one side in an axial direction of rotation shafts thereof, a communicating portion disposed on a first end side on which an input gear is disposed, to fall the developer from the upper developer conveyor to the lower developer conveyor, bearings to receive end portions the upper and lower developer conveyors, and first and second end seals to seal gaps in the bearings on the upper and lower developer conveyors, respectively. The first end seals and the second end are disposed on the first end side and a second end side, respectively. A sliding friction between the rotation shaft and at least one of the first end seals is smaller than a sliding friction between the rotation shaft and the second end seal.

A developing device includes a developing container including a first conveyance chamber and a second conveyance chamber disposed above the first conveyance chamber, a first stirring-conveyance member which conveys developer in the first conveyance chamber in a first direction, a second stirring-conveyance member which conveys the developer in the second conveyance chamber in a second direction opposite to the first direction, and a developer carrier. A second communication portion is formed which allows the first and second conveyance chambers to communicate with each other at their end portions on a downstream side in the second direction. In the first conveyance chamber, a guide member is disposed which guides, to the downstream side in the first direction, the developer passing through the second communication portion to fall into the first conveyance chamber.

A developing device includes a developer container that accommodates an electrostatic image developer including toner containing a toner particle and a zinc stearate particle, a ratio (D.sub.T/D.sub.S) of a volume-average particle size (D.sub.T) of the toner particle to a volume-average particle size (D.sub.S) of the zinc stearate particle being about 1.9 or more; a developer carrier that supplies the toner to an image carrier; a supply conveyor that supplies the electrostatic image developer while conveying the electrostatic image developer; a mixing conveyor that conveys the electrostatic image developer while mixing the electrostatic image developer; and a partition disposed between the supply conveyor and the mixing conveyor. The electrostatic image developer is moved from the supply conveyor to the mixing conveyor through a first passage and is moved from the mixing conveyor to the supply conveyor through a second passage.

A developing device includes a rotatable developer carrying member, first and second chambers configured to accommodate developer supplied to the developer carrying member, and first and second rotatable feeding members provided in the first and second chambers, respectively. A first communication port permits feeding of the developer from the second chamber to the first chamber, and a second communication port permits feeding of the developer from the first chamber to the second chamber. In addition, a toner content detecting portion includes a planar detecting surface including at least a planar coil generating a magnetic field and detects the toner content. The detecting surface is provided in the first communication port above a bottom of the first communication port and is disposed substantially in a central portion of the first communication port.

A developing device is provided which includes: a developing roller in contact with or facing an image hearer; a supply roller to supply toner to the developing roller; a casing; a first conveyer disposed within the casing and above the supply roller to supply toner stored in the developing device to the supply roller, while forming a first conveyance path; a second conveyer disposed within the casing with an upper end thereof positioned below that of the first conveyer, while forming a second conveyance path forming a toner circulation path together with the first conveyance path; a partition wall separating the first conveyance path and the second conveyance path in a longitudinal direction within a range excluding both longitudinal end portions; and a toner supply port, at a ceiling of the casing above the second conveyance path, through which toner is supplied to an inside of the developing device.

A developing apparatus includes a developing container to accommodate a developer and having first and second chambers divided by a partition wall for supplying the developer to a rotatable developing member and first and second communicating portions to allow the developer to move between first and second chambers by conveyance screws. A third communicating portion is disposed between the first and second communicating portions and above the conveyance screws to allow air inside the developing container to move between the first chamber and the second chamber. The developing container further includes a third chamber disposed above the second chamber in the vertical direction and accommodates initial developer in an unused state of the developing apparatus, and an opening portion for discharging the air inside the developing container to outside of the developing container is provided in the third chamber, with the opening being disposed above the third chamber.

A feeding screw for feeding a developer includes a rotation shaft, and a helical blade provided on the rotation shaft and including a plurality of threads. The feeding screw includes a first blade helically formed with a single thread on the rotation shaft, a second blade helically formed with a single thread on the rotation shaft, and a third blade helically formed with a single thread on the rotation shaft. With respect to a direction along the rotation shaft, a gap is provided between a downstream end portion of the second blade and an upstream end portion of the first blade. The gap is disposed corresponding to a region where the first blade is continuously formed.

A developing device includes a developing container including a first conveyance chamber and a second conveyance chamber disposed above the first conveyance chamber, a first stirring-conveyance member which conveys developer in the first conveyance chamber in a first direction, a second stirring-conveyance member which conveys the developer in the second conveyance chamber in a second direction opposite to the first direction, and a developer carrier. A second communication portion is formed which allows the first and second conveyance chambers to communicate with each other at their end portions on a downstream side in the second direction. In the first conveyance chamber, a guide member is disposed which guides, to the downstream side in the first direction, the developer passing through the second communication portion to fall into the first conveyance chamber.

A developing device including a holding body, a supply unit, a filling portion, a closing portion, and a duct portion is provided. The holding body holds a developer. The agitating unit agitates the developer. The supply unit supplies the developer that flows in from the agitating unit to the holding body. The filling portion is provided above the agitating unit and filled with the developer. The closing portion closes a lower portion of the filling portion, and causes the developer to drop from the filling portion into the agitating unit in a case where the closing portion is removed. The duct portion connects a space in the filling portion and a portion above the holding body.

A developing apparatus capable of suppressing an excessive discharge of developer from a developer discharge hole is disclosed. A first opening part through which developer is carried from a first case part to a second case part, and a developer discharge hole through which the developer is discharged are provided to the first case part. A first carrying member includes a counter blade between the first opening part and the developer discharge hole. The counter blade carries the developer in an opposite direction to a carrying direction of a first carrying blade of the first carrying member. A gap is prepared between an upper part of the counter blade and the first case part. A cross-sectional area of a discharge path for the developer from the counter blade to the developer discharge hole changes according to a progress of the developer along the discharge path.