PURPOSE: To obtain a reset signal for a processor and to perform resetting in case of malfunction by detecting edges of a signal outputted according to a programmed procedure, and detecting the level of the signal obtained by integrating the edges.

CONSTITUTION: Edges of the output signal of the microcomputer 1 are detected by a detecting circuit 2. The detected edges are integrated by an integrating circuit 3 and the 1st level detecting circuit 4 and the 2nd level detecting circuit 5 detects whether the integration output is within a specific range or not. When the output is not within the specific range, a resetting circuit 6 resets the microcomputer 1 to normal operation. Consequently, malfunction is detected speedily to perform resetting to a normal state speedily.