In a technique for restoring data damaged by a computer virus on a magnetic information recording disk in a hard disk drive, booting information required to boot the hard disk drive and file position information indicating the position of a file when data is stored in a file unit are backed up in a predetermined portion of a maintenance area on the disk. The booting information or the file position information is restored based on the backed up information when the booting information or the file position information is infected with the computer virus.