A CPU computes a maximum allowable time period for restoration of a sector in which an error occurs, on the basis of a command processing time period designated by a host, when the error occurs upon access to the disk designated by a command supplied from the host, the command processing time period enabling realtime processing. The CPU also determines the use of the computed maximum allowable time period as a maximum error retry time period. The CPU controls the retry of the sector within the determined maximum error retry time period.