A cartridge for being detachable from and attachable to a main casing of an image forming apparatus, the cartridge comprising: a frame defining an internal space for accommodating therein developing agent, the frame being formed with a filling port for filling the internal space with the developing agent therethrough; a rotation body having a rotation axis extending in a predetermined direction, the rotation body being provided at the frame and rotatable about the rotation axis relative to the frame; a driving force transmission unit provided at the frame and suitable for transmitting an external driving force from the image forming apparatus to the rotation body; a gear cover main portion including a detection opening; a closing member (39, 139) configured to close the filling port; and a moving member suitable for being irreversibly moved to one of a covered position and an exposed position by the external driving force transmitted through the driving force transmission unit, the moving member comprising a cover portion which is configured to cover at least a portion of the closing member (39, 139) when the moving member is at the covered position, and which is configured to expose the closing member (39, 139) when the moving member is at the exposed position, the cover portion being interposed between the detection opening and the closing member to cover the portion of the closing member in the covered position of the moving member, and not interposed between the detection opening and the closing member to expose the closing member through the detection opening to the outside of the cartridge in the exposed position of the moving member. a frame defining an internal space for accommodating therein developing agent, the frame being formed with a filling port for filling the internal space with the developing agent therethrough; a rotation body having a rotation axis extending in a predetermined direction, the rotation body being provided at the frame and rotatable about the rotation axis relative to the frame; a driving force transmission unit provided at the frame and suitable for transmitting an external driving force from the image forming apparatus to the rotation body; a gear cover main portion including a detection opening; a closing member (39, 139) configured to close the filling port; and a moving member suitable for being irreversibly moved to one of a covered position and an exposed position by the external driving force transmitted through the driving force transmission unit, the moving member comprising a cover portion which is configured to cover at least a portion of the closing member (39, 139) when the moving member is at the covered position, and which is configured to expose the closing member (39, 139) when the moving member is at the exposed position, the cover portion being interposed between the detection opening and the closing member to cover the portion of the closing member in the covered position of the moving member, and not interposed between the detection opening and the closing member to expose the closing member through the detection opening to the outside of the cartridge in the exposed position of the moving member.