PURPOSE: To make the density of a toner uniform by collecting a used developer, leading it to a toner replenishing and agitating part of a part which detached the circumferential surface of a carrier body, agitating and mixing said developer, and thereafter, leading it to a screw carrying means.

CONSTITUTION: An agitating and carrying part 29 agitates and mixes a developer carried from a screw carrying means 4, and a toner replenished from a toner replenishing means 5. An upper part 35a of a screw-shaped agitating shaft 35 screw-feeds the developer downwards. Also, a lower part 35b screw- feeds the developer upwards. As a result, in the agitating and carrying part 29, the developer is agitated and mixed, fed to the end part of a screw carrying means 6, and the developer is screw-carried. In this way, a developer whose mixing ratio of a toner and a carrier is uniform is supplied extending over the overall length in the axial direction of a developer carrier body, and a distinct picture can be formed.