PURPOSE: To prevent the active control abnormality caused by a bad environ ment by constituting the abnormality detection while executing the active control and the processing of the countermeasure with hardware but not software in an active controller.

CONSTITUTION: This device is provided so as to constitute an abnormality detection means detecting the fact that the active control becomes an abnormal state and outputting an abnormality signal and an output interruption means receiving the abnormality signal from the abnormality detection means and interrupting an output of an active control signal with the hardware. To put it concretely, the abnormality is detected by a mean voltage take-out device 14 obtaining the mean voltage value of the active control signal converted into an analog amount by rectification and smoothing, a comparator 16 comparing the mean voltage value with a prescribed DC voltage from a prescribed voltage generator 15 and a prescribed time controller 17 outputting the abnormality signal by judging it to it be in an abnormal state when the state is continued for a prescribed time after it is judged that the mean voltage value is the prescribed voltage value or above, is compared and decided by the comparator 16.