User data backup functions are realized through a computer, which is located on the management service provider corporation side and interfaces between a user side computer environment and a storage service side computer environment to support storage service. This computer selects storage devices which meet the user side conditions from a plurality of entirely or partially empty storage devices owned by the storage service side computer environment. The computer receives user data from the user side computer environment, divides the user data into records of a predetermined size and transmits the records to the storage service side computer environment so that the records are distributed and stored to the selected storage devices.