Patent ID: 8045900

Claim:
A developing device that houses a developing agent including carrier and toner, and that develops a latent image formed on an image carrier, comprising: transport members which have a screw portion formed on a shaft portion, and which transport the developing agent housed within the device in a longitudinal direction, and form a circulation path; supply means for supplying new carrier to the device; a discharge aperture, formed in a wall of a transport path of one of the transport members, discharging the developing agent outside the circulation path when a surface of the developing agent transported by the one of the transport members exceeds a predetermined height; and a bias path aperture, formed in the wall of the transport path of the one of the transport members and located upstream of the discharge aperture, the bias path aperture having a bottom at a higher level in the one of the transport members than a bottom of the discharge aperture, and diverting developing agent at a level higher than the bottom of the discharge aperture to another one of the transport members; wherein the one of the transport members includes an area in the longitudinal direction on which the screw portion is not formed, the discharge aperture is disposed opposite to the area on which the screw portion is not formed on the one of the transport members, and the length of the discharge aperture is formed smaller than that of the area in the longitudinal direction.