A hermetically sealed container is equipped inside thereof with: a melting furnace; a cooling roll for subjecting the molten metal tapped from the melting furnace to primary cooling to form a casting; and a rotatable cooling drum which receives the casting formed by the cooling roll and which subjects the casting to secondary cooling. The cooling drum has: a tubular member elongated in one longitudinal direction and having a receiving opening which is formed to open on one side of the tubular member to receive therein the casting, and a discharge opening which is formed to open on an opposite side of the tubular member to discharge the casting that has been subjected to the secondary cooling; and a transfer means for transferring the casting received from the receiving opening toward the discharge opening in response to the rotation of the tubular member.