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 development device includes a development container and a second agitation member. The development container includes a second transport chamber and a developer discharge port which is provided at the end portion of the second transport chamber on a downstream side. The second agitation member includes a second transport blade, a damming member which dams a developer, a regulation portion which transports the developer in a direction opposite to the second transport blade and a discharge blade which discharges the developer from the developer discharge portion. A second rotation shaft includes a large shaft diameter portion on which the second transport blade is provided, a small shaft diameter portion on which the regulation portion and the discharge blade are provided and a shaft diameter change portion. The damming member is arranged between the shaft diameter change portion and the end portion of the second transport blade on the downstream side.

A development device includes a development container, a first conveying member, a second conveying member, a toner concentration sensor, and a developer carrier. The first and second conveying members are equal to each other in outer diameter and shaft diameter, the outer diameter being 1.3 times the shaft diameter or more but 1.6 times the shaft diameter or less. Where L represents an axial length of the first conveying member, K represents a distance of a center position of the sensing surface of the toner concentration sensor from a downstream end of a first conveying chamber of the development container in the first direction, P represents a pitch of the conveying blade of the first conveying member, and R represents a rotational speed of the first conveying member, formula (1) is satisfied: 30000<(P×R×L)/K<45000 (1).

A development device includes a development container, a first conveying member, a second conveying member, a toner concentration sensor, and a developer carrier. The toner concentration sensor is arranged at a wall portion of the first conveying chamber in which the first conveying member is arranged. The first and second conveying members are equal to each other in outer diameter and shaft diameter, the outer diameter being 2.3 times the shaft diameter or more but 3.0 times the shaft diameter or less. Where D represents the shaft diameter of the first conveying member, L represents an axial length of the first conveying member, and K represents a distance of a center position of a sensing surface of the toner concentration sensor from a downstream end of the first conveying chamber in the first direction, formula (1) is satisfied: 500<(L.sup.2×K)/D.sup.4<2500 (1).

A developing device includes a developing container, a first stirring conveyance member, a second stirring conveyance member, and a developer carrying member. The developing container includes a first conveyance chamber and a second conveyance chamber that are arranged mutually side by side, and contains a two-component developer including a carrier and a toner. The first stirring conveyance member stirs and conveys the developer present in the first conveyance chamber in a first direction. The second stirring conveyance member stirs and conveys the developer present in the second conveyance chamber in a second direction. The developing container includes a toner replenishment portion that directly feeds a replenishment toner into the developer present in the first conveyance chamber from an upstream side of the first conveyance chamber with respect to the first direction. The carrier satisfies 0.73≤FR×AD/shape factor≤2.10.

A toner conveying device for conveying toner, comprising: a first conveying portion; and a second conveying portion conveying the toner conveyed from the first conveying portion. The first conveying portion further includes: a first screw which includes a first rotation shaft and a first blade portion, the first screw including an engaging portion and a first protruded portion on a first end portion; and a first conveying passage forming member having a first inner wall face which forms a first conveying passage. The second conveying portion includes: a second screw which includes a second rotation shaft and a second blade portion, the second screw including an engaged portion and a second protruded portion on a second end portion; and a second conveying passage forming member having a second inner wall face which forms a second conveying passage, and which is connected with the first conveying passage forming member.

An imaging system includes a developing chamber, a first conveyance path, a second conveyance path, a first air passage and a second air passage. A developing roller located in the developing chamber carries a developer to a developing region where the developing roller is closest to an image carrier. A first stirring-conveying portion is located in the first conveyance path adjacent the developing roller to supply the developer to the developing roller. A second stirring-conveying portion is located in the second conveyance path adjacent the first conveyance path to circulate the developer between the second conveyance path and the first conveyance path. The first air passage has an inlet coupled to the developing chamber and an outlet coupled to the second conveyance path, and the second air passage has an inlet coupled to the second conveyance path and an outlet coupled to the developing chamber.

A developing device includes: a first transport member and a second transport member that are disposed in a first transport path and a second transport path provided at an upper side and a lower side in a gravitational direction and that transport a developer so as to cause the developer to circulate between the first transport path and the second transport path; an ejecting mechanism that is provided in the first transport path disposed at the upper side in the gravitational direction and that ejects an excess developer; and a reverse helical section that is disposed in front of a support that supports the second transport member disposed at the lower side in the gravitational direction, the reverse helical section helically extending in a reverse direction relative to a helical section provided for circulating the developer, the developer being transported to the ejecting mechanism by the reverse helical section.

A developing device includes a first transport member and a second transport member that are respectively disposed in a first transport path and a second transport path arranged in a vertical direction and that transport developer so as to circulate the developer between the first transport path and the second transport path; a developing member that is disposed to face the first transport path and that receives the developer from the first transport path; and a third transport member that is disposed in a third transport path through which the developer that has not been used by the developing member is collected and transported to the second transport path. A central shaft of the second transport member is disposed farther in a vertically upward direction than is a central shaft of the third transport member.

A developing device includes a first transport member and a second transport member that are respectively disposed in a first transport path and a second transport path arranged in a vertical direction and that transport developer so as to circulate the developer between the first transport path and the second transport path; a developing member that is disposed to face the first transport path and that receives the developer from the first transport path; and a driving device that operates such that a relative speed ratio between a rotational speed of the developing member and a rotational speed of the second transport member is changeable.