PURPOSE: To speed up the recovery to normal operation by detecting edges of an output signal of a specific period to be processed in time series, and resetting a processor when the level of the signal generated by integrating the edges is larger than a set value.

CONSTITUTION: The output signal of a microcomputer 1 is supplied to an edge detecting circuit 4 to detect edges. Its edge detection output is integrated by an integrating circuit 8 to detect whether the integral output is within a specific level range set by a 2-level detecting circuit 10 or not. When the output is not within the specific level range, a flip-flop 13 is triggered and the microcomputer 1 is reset through a resetting circuit 3. Consequently, the recovery from abnormal operation to normal operation is performed speedily.