To judge the normality or failure of a driving means or an opening/ closing means by forcefully feeding an abnormal control instruction to the driving means, and detecting the failure of the driving means or the opening/ closing means based on the operation information of the opening/closing means at this time with a control means.

A CPU 28 in an ECU 20 serving as a control means calculates the rear wheel helm angle target value based on the front wheel steering angle change rate and other detection values. A driver CPU 42 which is a driving means generates a low-level relay control signal via the control instruction based on the rear wheel steering angle target value used as the dummy rear wheel steering angle target value, and whether a relay 50 which is an opening/ closing means is opened or not is judged. The voltage value of a terminal P connected to the relay 50 is received, and whether the voltage value is smaller than a fixed voltage threshold value or not is judged. If the voltage value is not smaller than the voltage threshold value, the relay 50 is judged as normal, and a driver ECU 40 is judged to have a failure.