A structure of a toner cartridge removably mounted on a developing unit of an image forming apparatus. Once a toner end mode is set due to the exhaustion of toner which is accommodated in the toner cartridge, it is prevented from being reset unless the empty cartridge is replaced with a full toner cartridge. The toner cartridge has a member capable of resetting a toner end mode only when the cartridge is loaded in a cartridge container for the first time. This member is cut off or permanently deformed when the toner cartridge is inserted into the cartridge container.