PURPOSE: To constitute a car motion controller of a few number of part items as well as to maintain the steering stability of a traveling car.

CONSTITUTION: In order to maintain the steering stability of a car in traveling, an axial yaw rate of the car is measured. A proper desired yaw rate is determined on the basis of an actual yaw rate of the car measured, and a direction of a tire is regulated so as to make the actual yaw rate approximate to the desired yaw rate. This tire direction is usually regulated by operation of a steering wheel, but in addition to this, it is regulated by a motor 22 being driven by a controller 32 separately from the operation of the steering wheel. As for this motor, a hydraulic motor 50 and an electric motor 22 are usable as well.