A toner cartridge for storing toner to be supplied to an image forming apparatus, includes a container in which the toner is stored and including a first wall having a filling port through which the toner is filled, and a second wall having a ventilation port sealable by a plug, the plug sealing the port during operation of the cartridge and is removed during maintenance of the cartridge to enable air to be supplied into the container through the port, a paddle configured to rotate to stir the toner between the first and second walls of the container, and a paddle gear connected to the paddle and through which a rotation force is transmitted to the paddle. The gear has a through hole that aligns with the ventilation port in a first direction parallel to a rotation axis of the gear when the gear is at a predetermined rotational position.