PURPOSE: To prevent the destruction of the specific data by inhibiting the write of data into a memory area storing the specific data when a write mode is erroneously set at a nonvolatile memory which can be electrically rewritten with the malfunction of a control circuit that is caused with the ON/OFF operations of a power supply or in a transient state like an instantaneous power failure state, etc.

CONSTITUTION: A memory cell array 2 includes the memory areas 2a and 2b where a start address SA and an end address EA of a specific data writing area are held. A comparator 9 compares both addresses SA and EA stored in the areas 2a and 2b with an address IA inputted for a write access and decides whether a rewritable area exists or not.