Provided is a backup device, etc., that updates copy data appropriately. A backup device 300, which records as copy data a copy of original data stored in multiple storage devices 110A to 110D, comprises: a write data storage unit 132, for receiving and storing write data to be written to the original data; and an updating unit 134, for using the write data to update the copy data when update permission data, which permit the use of the write data to update the copy data, are externally received.