When a blank DVD-RW disk is loaded into an optical disk drive, a host computer issues a FORMAT command to the disk drive. The optical disk drive having received the command performs quick formatting pursuant to a standard. Subsequently, the host computer issues a WRITE command to the optical disk drive in an idle time thereof, thereby instructing recording of dummy data. Consequently, an advantage analogous to that yielded as a result of background formatting of a DVD+RW disk is yielded, and the entirety of the DVD-RW disk can be formatted readily.