PURPOSE: To prevent the destruction of content of storage in a memory protection area at a failure, by providing a means which can designate the memory protection area in the hardware, by means of jumpers.

CONSTITUTION: In designating a memory protection area with a software instruction so that the content of a storage device can not be destructed, parts shown in broken lines (b) of a jumper set circuit 9 are jumpered. In fixing the hardware, parts as shown in a broken line (a) of the circuit 9 and a broken line (c) for the output of an access area selection circuit 8 for the area to be memory-protected, are jumpered. That is, an output of a memory address comparison circuit 2 set with the software instruction is inactivated as the broken line (a) of the circuit 9 and an arbitrary protection area is jumpered with one or a plurality of designations for the broken line (c) of the circuit 9.