In a toner cartridge, a cover member is attached to an outer surface of a case main body so as to cover a filling hole through which a toner is filled in a toner chamber. The cover member is detachably attached to the case main body by a lock mechanism disposed between the case main body and the cover member. The lock mechanism includes two or more lock structures which lock the cover member to the case main body and a release tool which carries out a release operation of the lock structures. Each of the lock structures includes an elastic engagement claw and an engagement recess which are provided on opposite surfaces of the case main body and the cover member, respectively. The release tool is configured to allow all of the elastic engagement claws to be simultaneously displaced in a lock release direction.