PURPOSE: To improve an stirring effect to prevent the leakage of a developer and to suppress the emission of an odor by providing a pump mechanism, jetting and stirring a wet type developer inside a storage part.

CONSTITUTION: When development is started, a developing roller 2 is imparted with driving power via a gear 4 from a driving source and rotated. On the other hand, the developer 5 is circulated accompanying with the action of a pump 9, and extension/contraction movement is carried out between A and B. When a pump part 10 carries out an extending action to obtain the state of the A, the developer 5 is sucked. When the pump part 10 is contracted to obtain the state of the B, the developer 5 is ejected from the pump 9. By consecutive actions, the jet stream of the developer 5 is generated in the big arrow direction inside the storage part of a developing unit 3, a carrier constituting the developer 5 and toner are stirred and mixed, and a developing liquid having uniform electrification is produced. Therefore, the stirring of the developer 5 is carried out by the circulating action and jetting power of the developer 5, so that a stirring mechanism is simplified. Thus, the excellent stirring effect is obtained, the leakage of the developer 5 is prevented, and simultaneously, the emission of the odor can be suppressed.