An image forming apparatus (1) includes a casing (21) having a toner conveyance path (34); a screw (24) conveying a toner in the toner conveyance path (34) in a predetermined conveyance direction; and a downstream side bearing (25) rotatably supporting a downstream side end portion of the screw (24) in the conveyance direction, wherein the screw (24) includes: a shaft (51) extending in the conveyance direction; and a spiral fin (52) provided around an outer circumferential face of the shaft (51), the shaft (51) has a downstream side insertion part (54) inserted into the downstream side bearing (25), and the downstream side insertion part (54) has an outer diameter larger than an outer diameter of a downstream side end portion of the fin (52) in the conveyance direction.

An example developing device includes a housing to contain a developer and having an opening, a developing sleeve provided in the housing and partially exposed to the outside of the housing through the opening, a magnetic member including a plurality of magnetic poles and located inside the developing sleeve, and an elastic member blocking an inflow of air through a space between a downstream edge of the opening in a rotation direction of the developing sleeve and an outer circumferential surface of the developing sleeve. The elastic member includes a fixed portion fixed to the housing at a position adjacent to the downstream edge of the opening and an extension portion extending from the fixed portion in a bent form in the rotation direction of the developing sleeve to be elastically in contact with the surface of the developing sleeve.

A developing device includes a developer carrying member for carrying and feeding a developer, first and second chambers for circulating the developer, and a partition wall. A first feeding member feeds the developer in the first chamber in a first feeding direction, and a second feeding member feeds the developer in the second chamber. The second feeding member includes a shaft, a first helical portion for feeding the developer in a second feeding direction, and a second helical portion for feeding the developer in the first feeding direction. The second helical portion is provided on the shaft and provided downstream of the first helical portion via a region where no helical portion is provided. A rib is provided on a first inner surface of the second chamber, with the rib disposed opposite the region where no helical portion is provided and extending upwardly in a vertical direction.

In a developing device in which initial developer is sealed in and a developer discharge mechanism (a trickle mechanism, or an ACR mechanism) is provided, the driving-torque load generated in the developing device is suppressed, regardless of the state of distribution of the developer that is sealed in the developing device. The order of releasing seals provided over openings is defined as follows. First, a seal provided on the downstream side of a stirring chamber starts to be released. Then, a seal provided over a discharge port is released. Lastly, a seal provided on the upstream side of the stirring chamber starts to be released.

A developing apparatus is provided with a third communication port downstream of a first communication port of a partition wall. The third communication port is disposed at a position facing a return screw when viewed from a horizontal direction. A lower end of the third communication port is located above a lower end of the first communication port. Because the first communication port is practically enlarged to the return screw, the delivery of the developer from an agitating chamber to a developing chamber is not suppressed even if fluidity of the developer drops. Accordingly, the developer is hardly rotated with a developing sleeve. Still further, because a partition wall prevents the developer from entering the third communication port, the discharge of the developer is hardly suppressed. This arrangement makes it possible to reduce an occurrence of image defect caused by the delivery and discharge of the developer.

An agitating screw at a first communication port delivering a developer from a collecting chamber to a developing chamber is formed to be a multiple-threaded screw. The use of the multiple-threaded screw makes it possible to increase a developer surface level at the first communication port. If the developer surface level becomes too high within the collecting chamber, an image defect caused by entrainment of the developer by the developing sleeve may occur. Then, an arrangement is made such that the developer surface level does not become so high that may cause the entrainment of the developer by accelerating delivery of the developer at the first communication port. Thus, the use of the multiple-threaded screw makes it possible to accelerate the delivery of the developer and to reduce an image defect otherwise caused by the entrainment of the developer.

A developing apparatus includes: a developer tank that contains a developer; and conveyance members that convey the developer while agitating the developer. The conveyance members include a first screw and a second screw. The developer tank includes: a first storage chamber in which the first screw is provided; a second storage chamber in which the second screw is provided; a partition that separates the first storage chamber from the second storage chamber; and a flow area that opens the partition to flow the developer between the first storage chamber and the second storage chamber; a developer detection sensor that detects an amount of the developer thereof; a discharge port that discharges the developer; and a discharge guide that guides the developer to the discharge port. The developer detection sensor detects that the developer tank is full according to the amount of the developer.

A developing device includes a housing, a developing roller, a developer stirring member, and a layer thickness regulating member. The developing roller includes a stationary magnet and a sleeve. The stationary magnet includes a first magnetic pole having a specific polarity, and a second magnetic pole lying downstream of the first magnetic pole and having the same polarity as the first magnetic pole. In an entire inter-pole region between the first magnetic pole and the second magnetic pole, the stationary magnet produces a magnetic force including a horizontal component that keeps the specific polarity and has a value greater than zero (mT). The inter-pole region includes a flat area where a horizontal magnetic force component having a minimum absolute value exits and the horizontal magnetic force component changes within a range of 0.5 (mT) or less, the flat area extending over a range of 10 degrees or more.

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 powder transport device includes: a rotation shaft rotatably supported in a container chamber that contains powder; and plural blade members detachably attached to the rotation shaft, the blade members including spiral blades configured to transport the powder in an axial direction of the rotation shaft in response to the rotation shaft rotating.