A download method comprises an auxiliary downloader storing step for storing an auxiliary downloader 38 in a storage unit by executing a downloader 22 stored in the storage unit, a new software storing step for storing new software 40 in a region of the storage unit other than the storage region where the auxiliary downloader 38 is stored, and a downloader starting step for executing the auxiliary downloader 38 in the event of failure of the storage of the new software 40.