To surely protect execution codes or data for an information processor which are stored in a storage device such as a rewritable memory.

Whether operation is writing operation in a set address range or not is checked (S101), and when the operation is the writing operation in the set address range, writing processing is executed (S102). Then whether the writing is to be informed of or not is judged (S103), and in the case of informing of the writing, the execution of the writing operation is informed of, and when notification is unnecessary, the operation ends as it is. When the operation is not the writing operation in the set address range, data or the like are written in an address range other than the set address range (S105). In the processing, the permission of notification of writing processing can be selected, and by selecting the ON/OFF of issue permission of an interruption signal or the ON/OFF of status display permission by software setting, a CPU 1 can be informed of the generation of writing operation in a specific address range.