PURPOSE: To set frequency that backup is executed in accordance with the significance of files, to set a backup processing to be efficient and to reduce a load.

CONSTITUTION: A client 10, a server 20 and a file server for backup 30 are connected through a communication network 40. A file management table 200 exists on the memory 21 of the server 20. Update counters recording the number of the update times of the files and the prescribed number of update times for executing backup in accordance with the significance of the files are set for the respective files in the file management table 200. The server 20 once stores input data from the client 10 in the management table 200 as latest information and stores in an external storage device 50. At that time, the update counter is updated, and the server 20 transmits the backup of the file to the server 30 when the number of update times coincides with the prescribed number of update times.