Patent ID: 7983590

Claim:
A developing unit comprising: a developer cartridge that is configured to accommodate developer and comprises a first opening for enabling communication between an inside of the developer cartridge and an outside of the developer cartridge; a housing comprising: a cartridge housing part for housing the developer cartridge; and a second opening that is provided in a position opposite to the first opening and is formed on the cartridge housing part; a shutter that comprises a third opening, the shutter being movable between an open position where the third opening is located at a position between the first opening and the second opening and a closed position where the third opening is apart from the positions of the first opening and the second opening; and a protruding portion comprising a flexible sheet that protrudes into the third opening from an upstream end portion of the third opening in a movement direction of the shutter from the open position to the closed position at the side close to the first opening, the protruding portion further comprising a first end at a side close to the first opening and a second end at a side close to the second opening, the first end protruding more downstream in the movement direction than the second end.