The invention provides an application technique of a backup data in which a backup data can be utilized by creating a backup data including no indeterminate data in a backup system. In a backup system including a primary system and a backup system, the method of creating the backup data includes: a data update record rerun step for rerunning a data update record to a backup data; and a backup data creation step for starting a read to a backup data B, stopping a read to a backup data A, copying the backup data to the backup data A, starting the read to the backup data A, stopping the read to the backup data B, and copying the backup data A to the backup data B.