and measuring its frictional force by frequency analyzing the sound from the tires or by projecting light upon the road surface and evaluating the reflection of the light from the road surface generally the yaw rate or the lateral acceleration of the vehicle for a certain steering input is selected as an object for evaluating the driveability of a vehicle therefore by detecting the yaw rate and so on and controlling the steering angle ratio of the rear wheels according to such detection results even more accurate control of the driveability of the vehicle becomes possible fig4 is a functional block diagram of another embodiment of the control device for the front and rear wheel steering device based upon such a recognition the outputs x y m u and z of the front wheel steering angle sensor 14 the rear wheel steering angle sensor 15 and the vehicle speed sensor 17 and the running condition sensor 19 are inputted to a computation process a the memory b internally provided in a computer 19 stores a mathematical function w 0 f x y m u z which gives a target yaw rate w 0 of the vehicle for each combination of the front wheel steering angle signal x the vehicle speed signal u the running condition signal z and the target rear wheel steering angle.