It is an object to eliminate possibilities in which newest backup data cannot be created owing to overwriting of data update records when performing backup using a duplicating system. The data backup system, including an active system as a computer system of a backup source and a standby system as a computer system of a backup destination, is provided in such that a communication settings judging section is provided in the standby system for actively changing settings of a data communicating section for transferring data update records to thereby prevent overwriting of portions among data update records that are necessary for creating newest backup data.