A toner case includes a case main body, a conveying member and a transmitting member. The case main body is configured to store a toner and has a discharge port for the toner. The conveying member is configured to rotate around a rotation axis extending along a rotation axis direction and to convey the toner in the case main body to the discharge port. The transmitting member is configured to transmit rotation to the conveying member. The conveying member is movable along the rotation axis direction with respect to the transmitting member between a coupling position where the conveying member is coupled to the transmitting member and a release position where a coupling of the conveying member to the transmitting member is released.

A developing device includes a developer tank holding a developer, and a transporting member stirring and transporting the developer. The transporting member includes first and second screws each provided with a rotary shaft having a spiral blade disposed on an outer circumferential face of the rotary shaft. The first and second screws are disposed such that the rotary shafts are parallel to each other. The developer tank includes a first compartment accommodating the first screw, a second compartment accommodating the second screw, a partition separating the first compartment and the second compartment, and a circulation zone. The circulation zone includes an opening in the partition that allows the developer to flow through. The first and second compartments have bottom faces at different heights. A protrusion is formed on a bottom face in the circulation zone.

A toner cartridge includes a first casing, a second casing, an auger screw, and a shutter. The first casing has a first internal space. The second casing has: a second internal space smaller than the first internal space; a first opening allowing toner in the second internal space to be discharged; and a second opening allowing air in the second internal space to be sent to an outside. The auger screw is rotatable about a first rotation axis and configured to convey toner in the first internal space to the second internal space. The shutter is rotatable relative to the second casing about a second rotation axis between a first position in which the shutter closes the first opening and a second position in which the shutter opens the first opening. In a state where the shutter is at the second position, the shutter does not close the second opening.

A toner supply device includes a toner storage unit that stores toner for supply, and a stirring unit that stirs the toner stored in the toner storage unit. The toner storage unit includes an inlet for introducing the toner from a toner container to the toner storage unit, and an intake portion that takes in the toner to a supply path for supplying the toner toward a developing device. The stirring unit includes a paddle portion provided to be rotatable about an axis of rotation for moving the toner toward the intake portion, and a screw portion for transporting the toner toward the paddle portion. The screw portion transports the toner in a direction of the axis of rotation of the paddle portion.

A transporting member includes a rotating shaft and plural helical blades that helically extend around the rotating shaft and that transport a transport object in a direction of the rotating shaft as the rotating shaft rotates, each helical blade including a downstream side surface at a downstream side in a transporting direction and an upstream side surface at a side opposite to the downstream side surface. A portion of at least one of the helical blades has a gap that enables the transport object to move in the direction of the rotating shaft, and the at least one of the helical blades includes an upstream section that extends upstream in a rotating-shaft rotation direction, in which the rotating shaft rotates, from the gap. The upstream section includes a portion in which an inclination angle of the downstream side surface is less than an inclination angle of the upstream side surface.

A developing device includes a developer container, a developer carrier, first and second stirring/transporting members, a driving motor, first and second magnetic permeability sensors, and a control portion. The first magnetic permeability sensor is arranged in a first conveying chamber in the developer container, in a region other than a part facing a communication portion and senses the toner concentration in developer in the developer container. The second magnetic permeability sensor is arranged in a second conveying chamber in the developer container, in a region between a regulating portion and a downstream end of the developer carrier in the second direction. The control portion controls the supply amount of developer based on the output value of the first magnetic permeability sensor, and calculates the stable volume of developer in the developer container based on the difference between the output values of the first and second magnetic permeability sensors.

A conveyance screw includes a shaft member, a first blade and a second blade each formed helically on a circumference of the shaft member. The first blade includes a first wide portion and a first narrow portion both located within an area in the axial direction where both of the first blade and the second blade are provided. The first wide portion is protruded radially outward from the shaft member to a first outer diameter. The first narrow portion is formed continuously with the first wide portion in a winding direction of the first blade around the shaft member, and is protruded radially outward from the shaft member to a second outer diameter that is smaller than the first outer diameter.

A developing device includes an agitating transport device, a density detecting device, and an attracting device. The agitating transport device has a transport path and transports developer including a magnetic carrier while agitating the developer. The density detecting device detects density of the developer in the transport path of the agitating transport device. The attracting device is provided in the agitating transport device and has magnetic poles of one and another polarities exposed to the transport path facing the density detecting device so as to attract the developer by a magnetic force.

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 developing device includes a developer container, a developer carrier, first and second stirring/transporting members, a driving motor, first and second magnetic permeability sensors, and a control portion. The first magnetic permeability sensor is arranged in a first conveying chamber in the developer container, in a region other than a part facing a communication portion and senses the toner concentration in developer in the developer container. The second magnetic permeability sensor is arranged in a second conveying chamber in the developer container, in a region between a regulating portion and a downstream end of the developer carrier in the second direction. The control portion controls the supply amount of developer based on the output value of the first magnetic permeability sensor, and calculates the stable volume of developer in the developer container based on the difference between the output values of the first and second magnetic permeability sensors.