An amount-of-remaining-toner detecting device includes: a toner housing portion in which a toner bottle is housed, the toner bottle having a bottle body that is cylindrical and in which toner is housed, and a cap that is attached to one end of the bottle body in an axial direction of the bottle body and from which the toner housed in the bottle body is discharged; and circuitry configured to detect an amount of remaining toner in the toner bottle housed in the toner housing portion. The toner housing portion includes a first pair of electrodes facing each other with the bottle body interposed between the first pair of electrodes, and a second pair of electrodes facing each other with the bottle body interposed between the second pair of electrodes, at respective positions closer to the cap than the first pair of electrodes are. The circuitry detects the amount of remaining toner in the bottle body, based on at least one of a capacitance value between the first pair of electrodes or a capacitance value between the second pair of electrodes.

A first development chamber accommodates an agitator. A second development chamber accommodates a development roller and a supply roller. The second development chamber is located above the first development chamber. A toner cartridge contains toner to be supplied to the first development chamber. A transfer device is located above a photosensitive drum in a state where a drum unit is attached to a main housing. The transfer device transfers toner on the photosensitive drum to a sheet. An agitator includes a shaft and a blade. The shaft is rotatably supported by a development housing. The blade is rotatable together with the shaft. The blade has a first end fixed to the shaft and a second end located away from the first end. The agitator is configured such that, when rotated, the second end of the blade reaches a height of an opening in the development housing in a vertical direction.

An image forming apparatus includes a cartridge storage portion that is installed in an image forming apparatus main body, and a toner cartridge that is configured so as to be able to be inserted into and removed from the cartridge storage portion. The cartridge storage portion has a storage opening that receives the toner cartridge, and has a gap between an end part of the toner cartridge and the storage opening, through which the end part of the toner cartridge is not able to be held, when the toner cartridge is stored in the cartridge storage portion.

An image forming apparatus includes a toner container, a container attachment portion, and a control portion. The toner container has a coupling portion. The container attachment portion includes a coupled portion that includes a first key member. A second key member of the coupling portion is formed at position where it does not interfere with the first key member in attachment state. The second key member is made of insulator. The coupled portion includes a contact terminal in which a contact is opened by the second key member and becomes OFF state when the toner container is inserted to attachment position, and the contact is closed and becomes ON state when the toner container is removed from the attachment position. The control portion detects the toner container attached to the container attachment portion when the contact of the contact terminal changes from the ON state to the OFF state.

A toner supply device for supplying toner to a developing device includes a toner container containing toner to be supplied to the developing device and a remaining amount sensor for detecting the remaining amount of toner in the toner container. The toner container includes a cylindrical rotating container having a spiral conveying rib formed on the inner peripheral surface thereof and a paddle provided so as to be slidable on the inner peripheral surface of the rotating container. The remaining amount sensor detects the remaining amount of toner on the upstream side on or before the contact position of the paddle in the toner conveying direction.

A cartridge includes: a housing; a storage medium including an electrical contact surface; and a storage medium holder holding the storage medium and movable relative to the housing. The storage medium holder is positioned at one end portion of the housing in a first direction and includes: a first holder holding the electrical contact surface; a second holder positioned spaced away from the first holder in a second direction crossing the first direction; and an elastic member expandable and shrinkable in the second direction between the first holder and the second holder. The first holder has a first hole penetrating the first holder in the second direction. The first hole is positioned farther from the housing in the first direction than the second holder and the elastic member are from the housing in the first direction and is overlapped with the electrical contact surface as viewed in the second direction.

An amount-of-remaining-toner detecting device includes: a toner housing portion in which a toner bottle is housed, the toner bottle having a bottle body that is cylindrical and in which toner is housed, and a cap that is attached to one end of the bottle body in an axial direction of the bottle body and from which the toner housed in the bottle body is discharged; and circuitry configured to detect an amount of remaining toner in the toner bottle housed in the toner housing portion. The toner housing portion includes a first pair of electrodes facing each other with the bottle body interposed between the first pair of electrodes, and a second pair of electrodes facing each other with the bottle body interposed between the second pair of electrodes, at respective positions closer to the cap than the first pair of electrodes are. The circuitry detects the amount of remaining toner in the bottle body, based on at least one of a capacitance value between the first pair of electrodes or a capacitance value between the second pair of electrodes.

A toner supply device for supplying toner to a developing device includes a toner container containing toner to be supplied to the developing device and a remaining amount sensor for detecting the remaining amount of toner in the toner container. The toner container includes a cylindrical rotating container having a spiral conveying rib formed on the inner peripheral surface thereof and a paddle provided so as to be slidable on the inner peripheral surface of the rotating container. The remaining amount sensor detects the remaining amount of toner on the upstream side on or before the contact position of the paddle in the toner conveying direction.

A first development chamber accommodates an agitator. A second development chamber accommodates a development roller and a supply roller. The second development chamber is located above the first development chamber. A toner cartridge contains toner to be supplied to the first development chamber. A transfer device is located above a photosensitive drum in a state where a drum unit is attached to a main housing. The transfer device transfers toner on the photosensitive drum to a sheet. An agitator includes a shaft and a blade. The shaft is rotatably supported by a development housing. The blade is rotatable together with the shaft. The blade has a first end fixed to the shaft and a second end located away from the first end. The agitator is configured such that, when rotated, the second end of the blade reaches a height of an opening in the development housing in a vertical direction.

A developing device develops an electrostatic latent image formed on a photosensitive drum. A bottle rotation sensor detects rotation of a toner bottle that stores toner. A bottle motor drives the toner bottle for rotation to thereby discharge toner from the toner bottle. A hopper-internal toner sensor detects presence/absence of toner stored in a hopper that stores toner discharged from the toner bottle. A replenishment unit replenishes toner stored in the hopper to the developing device. Which of failure of the bottle rotation sensor and rotation failure of the toner bottle has occurred is determined based on a detection result of the bottle rotation sensor and a detection result of the hopper-internal toner sensor.