Patent ID: 7561835

Claim:
A developing device, comprising: a developing unit configured to develop an electrostatic latent image with a toner; a toner cartridge configured to contain the toner and supply the toner to the developing unit, and including a rotatable agitator configured to agitate the toner by rotating through the toner, wherein the toner cartridge is detachably attached to the developing unit; at least one opening configured to pass the toner between the developing unit and the toner cartridge; and at least one control valve configured to face the at least one opening and control transport of the toner through the at least one opening by contacting with the agitator as the agitator rotates through the toner, wherein a toner replacement ratio (b/a) of the developing device satisfies relationship: 0.05 ≦b/a≦ 2.0 wherein a represents an amount of the toner supplied to the developing unit from the toner cartridge per a unit time and b represents an amount of the toner discharged to the toner cartridge from the developing unit per the unit time.