PURPOSE: To increase the detection accuracy of an apparatus which estimates the cornering power of a tire and which detects the yaw rate of a vehicle on the basis of its estimated value as well as the running speed and the steering angle of the vehicle.

CONSTITUTION: Air pressures of tires at individual wheels are detected by tire-pressure detection parts 3, the average tire pressure of the right and the left front wheels and the average tire pressure of the right and left rear wheels are operated respectively by individual average-tire-pressure operation parts 4. According to the relationship between the tire pressures and cornering powers, the individual average cornering powers are operated by individual average-cornering-power operation parts 5 according to the individual operated tire pressures. On the basis of the individual operated cornering powers, of a running speed detected by a running-speed detection part 1 and of an actual steering angle detected by an actual-steering-angle detection part 2, the plane-2 degree-of-freedom linear model of a vehicle is assumed. Thereby, the target yaw rate of the vehicle is operated by a raw-rate operation part 6. Since the cornering powers are estimated by taking into consideration a change in the tire pressures and the target yaw rate is detected, the detection accuracy of the title detection apparatus is enhanced.