PURPOSE: To reduce the input/output load of a medium and a device where a file exists by quicking the processing of medium release.

CONSTITUTION: At the time of processing a file assignment 2 concerning a file 1, a device medium ensuring means 5 prepares a device medium management table 4. If there is no designation of continuous use in a job step followed by the file 1, a device medium release means 6 erases a device medium management table 4 at the time of processing a file de-assignment 3. At the time of the requirement of the medium release requirement, a medium release advisability deciding means 8 certifies the presence/absence of the device medium management table 4 to device the advisability of the release of the medium.