FIGS. 6A to 6C are explanatory drawings showing a connecting and disconnecting member for changing the relation of the rotatable developer discharge member of the developer cartridge Ky with the gear G5 between the disconnected state in FIGS. 4A and 4B, and the connected state in FIGS. 5A and 5B. FIG. 6A is a side view, FIG. 6B is a plan view when viewed in the direction indicated by an arrow VIB