With a plurality of memory blocks as a pair, a plurality of pairs of the memory blocks are provided and in a case where a pair of memory blocks is designated as a new boot region, when designating other pair of memory blocks as a boot region, a value obtained by subtracting a predetermined value from an initial value set at the boot area designation flag of the memory block of all the memory block pairs is stored in the boot area designation flag of each memory block of other memory block pair and at the time of booting the system, if values of the boot area designation flags in the memory blocks of other memory block pair are equal and not the initial value, determination is made that a boot program is stored in other memory block pair.