Abstract: A container body of a concrete cask includes a storage portion that stores a canister. A refilling system includes a reduction cylinder having an outside diameter smaller than the diameter of the storage portion and an inside diameter larger than the diameter of the canister, a first lift mechanism configured to raise and lower the reduction cylinder between a down position in the storage portion and an up position wherein it is drawn out of the storage portion, and a second lift mechanism having a holding portion for holding one end portion of the canister and configured to raise and lower the canister with respect to the container body. In refilling operations, the canister is loaded into and unloaded from the storage portion of the container body by the second lift mechanism with the reduction cylinder set in the storage portion.