A disk apparatus has a memory storing boot-information; and a stop section which reads, upon receipt of a stop event, the boot-information from a disk and checks the read information against the boot-information in the memory. This section updates contents of the memory to store therein the same boot-information as that in the disk and writes flag-information indicating that the same boot-information is stored in the memory when a difference is found by the checking. The apparatus also has a start section which judges, upon receipt of a start event, whether or not the flag-information is stored in the memory, reads the boot-information from the memory and activates a device used with the apparatus while deleting the flag-information when the flag-information is stored. This section reads the boot-information from the disk to activate the device and writes the read boot-information in the memory when the flag-information is not stored.