To determine a turn state of a vehicle with certainty by computing radius of turning from speed difference between right and left wheels, a tread value, and vehicular speed, computing the centrifugal force from the radius of spinning, and determining the turning of the vehicle when the centrifugal force is more than the specified value.

When an automobile 1 curvingly runs in the direction of an arrow A, speeds V1, V3 of left wheels 2a, 2b exceed speeds V2, V4 of right wheels 2b, 3b due to difference of radii of spinning. That is, V1-V2=Δ1>0, V3-V4=6≥2>0. When the values Δ1 and Δ2 are both more than zero for a specified time or longer, their mean value is read in a computer for centrifugal force calculation. Speed of a vehicular body is estimated from an output of the wheel speed sensor to compute the radius of spinning. The centrifutal force is then computed. When the specified value or more of centrifugal force is applied for a specified time or longer, spinning of the vehicular body is determined.