When a steady straight advancing state presuming device presumes that the vehicle is in a steady straight advancing state, and a slip rate calculating device calculates a small slip rate, based on an output from a driving-state detecting device, or when the steady straight advancing state presuming device presumes that the vehicle is in the steady straight advancing state, and a driven wheel torque calculating device calculates a small driven wheel torque, based on the output from the driving-state detecting device, a correction execution determining device determines that the vehicle is in a stable state suitable for correcting the wheel speed. By a command from the correction execution determining device, a correcting device corrects the driven wheel speed or the follower wheel speed based on a speed ratio of the driven wheel speed to the follower wheel speed calculated by a speed ratio calculating device. Thus, when a different-diameter tire has been mounted on a wheel, it is possible to precisely correct the wheel speed without being influenced by the slipping of the driven wheels or by the turning of the vehicle.