To guarantee a band of file access of high priority while simultaneously processing a file access request of high priority and a file access request of low priority when two or more file access requests to the same storage device conflict with each other.

If file access of high priority is executed, middleware 22 issues to a file system 21a a second file access command within a surplus band obtained by subtracting a guaranteed band of the file access of high priority from the maximum band of a storage device 14. At that time, if the number of first file access command is one, the middleware 22 performs file access operation only during a predetermined partial period in each cycle, and if the number of first file access commands to be processed in parallel is N (N>1), performs file access operation only during a predetermined partial period in only one cycle out of N cycles.

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