Steering stability of a vehicle under a traveling state such as cornering is enhanced by controlling a state of the vehicle based on cornering powers of right and left wheels. A detecting unit 1 detects action force containing longitudinal force Fx, lateral force Fy and vertical force Fz which act on each wheel. A specifying unit 2 specifies a friction coefficient between the wheels and road surface. An estimating unit 6 estimates cornering power ka of each wheel based on the action force and the friction coefficient. A processing unit 7 determines control values so that the representative value ka_ave of the cornering powers concerning the right and left wheels is larger than the present value of the representative value ka_ave of the cornering powers concerning the right and left wheels. Controlling units 8 to 10 control the state of the vehicle based on the control values thus determined.