When an action for turning off the power of a host computer is performed, the host computer transmits control information to a disk drive to the effect that chucking should be canceled. Accordingly, the disk drive cancels chucking of a disk and transmits information to the host computer to the effect that cancel has been completed. Receiving the information to the effect that chucking has been canceled, the host computer terminates a disk drive application, confirms that all of the started applications are completed, and then terminates OS (Operating System).