DEVELOPING DEVICE

PROBLEM TO BE SOLVED: To provide a developing device which facilitates replenishing of toners and lessens waste in exchanging while preventing the occurrence of abnormal images. SOLUTION: The developing device 5 which has a developing section 5d for developing the electrostatic latent image of a photoreceptor belt 1 by toners and a toner cartridge 31 for supplying the toners to the developing section 5d and is attachable and detachable to and from a printer body is provided with the toner cartridge 31 in the developing section 5d freely attachably and detachably to and from the cartridge and the toners of the toner cartridge 5d are supplied through a toner replenishing port 37 to the developing section 5d. The toner replenishing port 5d is provided with a check valve 41 consisting of an elastic body to obstruct the back flow of the toners to the toner cartridge 31 from the developing section 5d.