An actual slip ratio of a wheel is estimated from a slip ratio speed of a wheel calculated according to a running state of a vehicle based on relationship between a slip ratio of the wheel of the vehicle and the slip ratio speed of the wheel set in advance. Typically, the actual slip ratio is estimated supposing that the slip ratio of the wheel calculated according to the running state of the vehicle, when a change rate of the slip ratio speed becomes larger than a predetermined value set in advance, is a reference slip ratio determined in advance according to the relationship between the slip ratio and the slip ratio speed set in advance. Therefore, it is possible to improve control accuracy when controlling a state of the vehicle by decreasing an effect of operation by a driver and a road surface, for example.