According to a first aspect of the present invention, there is provided a toner cartridge detachably mountable to a receiving device, the toner cartridge comprising a container including a accommodating portion for accommodating the toner and a discharge opening for discharging the toner from the accommodating portion into the receiving device; and an open/close member including a closing portion for closing the discharge opening and an engaging portion movable relative to the closing portion, the open/close member being rotatable relative to the container between (a) an opening position for causing the closing portion to open the discharge opening and (b) a closing position for causing the closing portion to close the discharge opening, wherein the engaging portion is movable relative to the closing portion between (c) a engaging position for engagement with the receiving device to receive a force for moving the open/close member from the opening position to the closing position when the toner cartridge is dismounted from the receiving device and (d) a retracted position retracted from the engaging position, and wherein the engaging portion is movable from the retracted position to the engaging position with rotation of the open/close member from the closing position to the opening position.