A developing device includes first and second chambers, a developing roller, first and second mixers, and one or more removable seals. The developing roller is in the first chamber. The first mixer is in the first chamber and configured convey developer in a first direction along a rotational axis of the developing roller. The second chamber is connected to the first chamber via a first port and a second port that are spaced apart from each other in the first direction. The second mixer is in the second chamber and configured to convey developer in a second direction opposite to the first direction. The one or more removable seals cover the first and second ports. A developer is contained in one of the first or second chambers. A developer discharge port is provided on the other one of the first or second chambers.

A developer conveyor includes a shaft; a first blade helically wound around the shaft in a first direction, a second blade disposed away from an end of the first blade with a gap in a longitudinal axial direction of the developer conveyor and helically wound around the shaft in a second direction opposite the first direction, and a third blade helically wound around the shaft in the first direction at least at a position where the gap is formed.

A feeding screw for feeding a developer includes a rotation shaft, a first blade portion helically formed on an outer peripheral surface of the rotation shaft to feed the developer in one direction, a second blade portion helically formed on the outer peripheral surface to feed the developer in the one direction, and a third blade portion helically formed on the outer peripheral surface to feed the developer in the one direction. The first blade portion and the second blade portion overlap with each other with respect to a rotational axis direction of the feeding screw, the second blade portion and the third blade portion do not overlap with each other with respect to the rotational axis direction, and the third blade portion and the first blade portion overlap with each other with respect to the rotational axis direction.

A developing device includes first and second chambers, a developing roller, first and second mixers, and one or more removable seals. The developing roller is in the first chamber. The first mixer is in the first chamber and configured convey developer in a first direction along a rotational axis of the developing roller. The second chamber is connected to the first chamber via a first port and a second port that are spaced apart from each other in in the first direction. The second mixer is in the second chamber and configured to perform convey developer in a second direction opposite to the first direction. The one or more removable seals cover the first and second ports. A developer is contained in one of the first or second chambers. A developer discharge port is provided on the other one of the first or second chambers.

A conveying screw configured to convey a toner in an axial direction includes a conveying shaft part and a conveying blade. The conveying shaft part is configured to be rotated around an axis. The conveying blade is spirally formed around an outer circumferential face of the conveying shaft part and configured to convey a toner in a replenishment path. At least one spiral of the conveying blade is formed by two semicircular blade plates which are coupled to in postures inclined in opposite directions to each other. A through hole through which the toner is passed in the axial direction is formed in an area surrounded by the conveying shaft part and the two blade plates.

A developer conveyor includes a shaft; a first blade helically wound around the shaft in a first direction, a second blade disposed away from an end of the first blade with a gap in a longitudinal axial direction of the developer conveyor and helically wound around the shaft in a second direction opposite the first direction, and a third blade helically wound around the shaft in the first direction at least at a position where the gap is formed.

A developing device includes a developer carrying member, a first chamber, a second chamber, a first communicating portion, a second communicating portion, and a feeding screw, provided in the second chamber, including a feeding portion having a first helical blade and including a returning portion having a second helical blade in the form of a plurality of threads, the feeding portion and the returning portion being provided so that a boundary portion therebetween opposes the second communicating portion. The first helical blade and the second helical blade satisfy the following relationship: P2P1, where P1 is a pitch, or lead, of the first helical blade and P2 is a lead of the second helical blade.

A conveying screw configured to convey a toner in an axial direction includes a conveying shaft part and a conveying blade. The conveying shaft part is configured to be rotated around an axis. The conveying blade is spirally formed around an outer circumferential face of the conveying shaft part and configured to convey a toner in a replenishment path. At least one spiral of the conveying blade is formed by two semicircular blade plates which are coupled to in postures inclined in opposite directions to each other. A through hole through which the toner is passed in the axial direction is formed in an area surrounded by the conveying shaft part and the two blade plates.

A feeding screw for feeding a developer includes a rotation shaft, and first, second, and third blade portions helically formed on the outer peripheral surface of the rotation shaft to feed the developer in one direction. The first blade portion and the second blade portion overlap with each other, the second blade portion and the third blade portion do not overlap with each other, and the third blade portion and the first blade portion overlap with each other, all with respect to the rotational axis direction of the feeding screw. A gap is provided between a downstream end of the second blade and an upstream end of the third blade portion in the one direction, and the gap is disposed within a region where the first blade portion is formed with respect to the rotational axis direction of the feeding screw.

A feeding screw for feeding a developer includes a rotation shaft, a first blade portion helically formed on an outer peripheral surface of the rotation shaft to feed the developer in one direction, a second blade portion helically formed on the outer peripheral surface to feed the developer in the one direction, and a third blade portion helically formed on the outer peripheral surface to feed the developer in the one direction. The first blade portion and the second blade portion overlap with each other with respect to a rotational axis direction of the feeding screw, the second blade portion and the third blade portion do not overlap with each other with respect to the rotational axis direction, and the third blade portion and the first blade portion overlap with each other with respect to the rotational axis direction.