PURPOSE: To enable the pursuit of program mistake in a short time, by producing an interrupting signal only when the program is not normal, in detecting the program number performing memory access incorrectly.

CONSTITUTION: When a memory is incorrectly rewritten, the address is set to an address set register 3 externally and the program number which rewrites it normally is set to a program number set register 5 externally to operate a computer. When an instruction rewriting the memory of the set address is executed, since the content of a memory address register 2 and the content of the address set register 3 are coincident, it is detected with an AND gate 6, the processing program number register 4 and a program number set register 5 are dissident with the content as an NAND gate 7 and an interrupting signal 10 is outputted with a timing signal 9.