To determine whether an unsteerable condition, if any, is caused by mere tire-stuck or failure in an electric system, by detecting the conditions of a wheel and steering wheel, determining the stopping of the steering operation of a steering wheel during wheel operation, and determining whether the condition is normal or abnormal based on load current.

An unsteerable condition is determined if the steering angle variation βD of a steering wheel per a fixed time is smaller than the steering angle variation β determined by the rotational angle α of a wheel per a fixed time (S106). The load-current of a motor for a driving apparatus is detected (S108). The detected value ID of load current is compared with a stored stall current value IS and, in the case of ID≥IS, determination is taken as normal or mere tire-stuck (S114). On the other hand, in the case of ID<IS, comparison is taken as a current set value IR slightly lower than the ID and IS (S118) and, in the case of ID<IR, determination is taken as some abnormality such as failure in an electric system (S124).