A file management system comprises a free-cluster queue describing cluster information indicating a cluster of a memory device in which “data has not been deleted yet but a file will be written preferentially only when a file write request is received”; means deleting, via a preferential input/output request queue in a driver, management information of data according to a deletion request for a file; means selecting either a non-preferential input/output request queue or the free-cluster queue to which the cluster information of the cluster in which the file whose management information has been deleted; means setting the cluster information of the data to which the deletion request is given, to either the non-preferential input/output request queue or the free-cluster queue, depending on selected results; and means providing the cluster information set in the free-cluster queue to a preferential input/output request queue of the driver, when a predetermined event occurs.