PURPOSE: To provide a method for monitoring two computers operating as redundnace in parallel, especially a microcomputer in which a, so called, monitor signal is sometimes supplied when each computer is correctly operated.

CONSTITUTION: A signal (WD1' or WD2') with the same length timely delayed from a monitor signal (WD1 or WD2) is generated, and those delayed signals are connected (NAD gate 8). The connected signal drives a time element (count stage 9), and when it is not preliminarily reset by the new connected signal even after the lapse of a prescribed time, the time element generates an alarm signal or an interruption signal.