A feeding screw includes a rotation shaft, and a plurality of blades helically formed with threads on the rotation shaft. The feeding screw includes a section in which a helix angle of each of the blades is not more than 56.5.

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 helical blade 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 third blade. A volume of the second blade is not more than 75% of the first blade between an upstream end portion of the second blade and the upstream end portion of the third blade with respect to the direction.

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 developer bearer, a casing defining an upper compartment to contain the developer and a lower compartment disposed lower than the upper compartment, to contain the developer, and a first conveyor and a second conveyor disposed in the upper compartment and the lower compartment, respectively, to convey the developer in a longitudinal direction of the developer bearer and circulate the developer between the upper compartment and the lower compartment through a first communicating opening, through which the developer is conveyed upward, and a second communicating opening. A developer-lifting range of the upper compartment, which opposes the first communicating opening, is larger in volume than a developer-lifting range of the lower compartment. One of the upper compartment and the lower compartment is disposed adjacent to the developer bearer to supply the developer to the developer bearer.

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 device includes a developer container, a developer carrier, and a stirring/conveying member. The developer container includes: a lower housing having a first accommodating portion and a first edge portion formed in a top end portion of it; and an upper housing having a second accommodating portion and a second edge portion formed in a bottom end portion of it. The first edge portion has a depression extending along the first edge portion, a first contact face formed inward of the depression, and a first opposite face formed outward of the depression. The second edge portion has an elevation inserted in the depression, a second contact face making contact with the first contact face, and a second opposite face facing the first opposite face. When the first and second contact faces are in contact, the first and second opposite faces face each other across a predetermined interval.

A developing device includes a housing in which a circulation path is formed by a first path through which a developer passed to a developing roll flows, a second path disposed offset from the first path in a direction of gravity, a pair of connecting ports connecting the first path and the second path, and a transport member that operates in the housing. The transport member transports the developer in a determined direction, or a reverse direction to the determined direction, in the circulation path according to a load applied for driving the transport member.

An image forming apparatus includes first and second image forming portions. A first conveying pipe conveys a first developer discharged from a first developing unit to a collection portion, and a second conveying pipe conveys a second developer discharged from a second developing unit to the collection portion. A first detection unit detects a toner content of the first developer in the first conveying pipe, and a second detection unit detects a toner content of the second developer in the second conveying pipe. The first developing unit can be removed from the image forming apparatus in a state that the first conveying pipe and the first detection unit remain in the image forming apparatus, and the second developing unit can be removed from the image forming apparatus in a state that the second conveying pipe and the second detection unit remain in the image forming apparatus.

A developing device includes a developing container and a second stirring member. The developing container includes a second feeding chamber and a developer discharge outlet disposed on the downstream side end of the second feeding chamber. The second stirring member includes a second feeding blade, a restricting part for conveying developer in the opposite direction to the second feeding blade, and a discharging blade for conveying the developer in the same direction as the second feeding blade so as to discharge the developer from the developer discharge outlet. The second rotation shaft includes a large shaft diameter part provided with the second feeding blade, a small shaft diameter part provided with the restricting part and the discharging blade, and a shaft diameter changing part positioned at a boundary between the large shaft diameter part and the small shaft diameter part.

A developing device has a developer container, a first stirring/transporting member, a second stirring/transporting member, a developer carrying member, a developer supply port, a developer discharge port, a regulating portion, and a height adjustment opening. The developer container has a partition partitioning between first and second transport chambers, and communication portions through which the first and second transport chambers mutually communicate. The first and second stirring/transporting members stir and transport developer in the first and second transport chambers in opposite directions respectively. The regulating portion regulates movement of the developer toward a developer discharge port. The height adjustment opening is formed in the partition, and when the height of the developer in the second transport chamber is equal to or higher than a predetermined height, part of the developer passes through the height adjustment opening and moves to the first transport chamber.