A developing unit includes a developer cartridge for accommodating developer and including a first opening, a first elastic member including a first through hole surrounding the first opening, a housing including a cartridge housing part and a second opening provided in a position opposite to the first opening, a second elastic member including a second through hole surrounding the second opening, and a shutter including a third opening and being movable between an opening position and a closing position. When the shutter is located at the opening position, an upstream end of the third opening in a movement direction of the shutter from the opening position to the closing position is located more upstream than upstream ends of the first through hole and the second through hole in the movement direction.