PURPOSE: To inform the outside of the occurrence of abnormality without interrupting other processes, by informing the outside of the abnormality when a processor makes access to a memory area other than those, whose programs are stored.

CONSTITUTION: When a noise occurs on an address bus or an instruction from a memory area other than those whose programs are stored due to a abnormality in hard or soft is read out, a processor cannot make normal operations. Therefore, an instruction fetching signal 204 and address decoder signal 205 from a decoder 5 are monitored by means of an AND circuit 9 at the time of instruction readout. Moreover, it is arranged that, when abnormality occurs, a priviledged interruption is inputted to the processor 1 as a mask-disable interruption process requesting signal 206 and the occurrence of the abnormality can be informed to the outside.