A recording area of a hard disk is managed by units. Each unit comprises physically continuous recording regions having predetermined size, and usage status of the unit is stored in an allocation unit (AU) management table. Data requiring a real time processing is stored in each unit. When the usage status of the unit is changed or modified due to the recording or deletion of data, the AU management table is updated and then information indicative of the fact that the AU management table has been updated is recorded. An apparatus where the final change is made is detected at the time the hard disk is inserted or a file system is initialized. And if the apparatus which last made the change adopts the file system which does not use the AU management table, then the table is reconfigured so as to retain the consistency of the AU management table.