Abstract: A developing unit including: a developing roller disposed in a developer tank in a location facing a recording medium; a supply passage for supplying developer to the developing roller; a shut-off device that is rotatable about the center axis thereof for opening and closing the supply passage; switching means that is provided with a spring clutch for transmitting rotational driving force to the shut-off device and is used for switching the shut-off device between the open and closed states; and a stopping position correcting mechanism for preventing variations in the stopping position of the shut-off device, the correcting mechanism having a clutch fixing plate mounted with screws on the outer wall of the developer tank in a slidable way around the center axis of the shut-off device and an engaging plate projecting from the clutch fixing plate and engaging with the case of the spring clutch.

Abstract: A developing apparatus which includes a developing section disposed to confront a recording medium for effecting development, and a device for supplying developing material to the developing section. The developing device is characterized in that there is mounted a stirring device rotatably provided in a supply passage for supplying the developing material to the developing section, and shutter plates are provided on an outer periphery of the stirring device so as to be controlled for rotation, thereby selectively closing or opening the supply passage.