In a developing apparatus, a housing has a first opening. A shutter is movable between an open position and a closed position. A locking member is movable between a lock position and a release position. The locking member is located between the housing and the shutter in a cartridge-attachment direction. The locking member is located at the lock position in a case where the toner cartridge is detached from the developing apparatus. The locking member is in contact with the toner cartridge, thereby moving from the lock position to the release position in a case where the toner cartridge is attached to the developing apparatus. A cover having a second opening that is in communication with the first opening in a state where the shutter is at the open position is located at an opposite side of the locking member with respect to the shutter in the cartridge-attachment direction.