PURPOSE: To continuously measure and detect the important dynamic characteristic quantity of a vehicle through an online system while using a method which can be made inexpensive and technically realized while using minimum sensors.

CONSTITUTION: The measured values of front steering angle δv, rear steering angle δh and transverse acceleration αy are supplied to a state estimator 1. The state estimator 1 is composed of a block 1.1 having adaptive filtering characteristics and a block 1.2 having an arithmetic conversion function and in this case, one data vector is formed from the said three measured values. Besides, an estimate corresponding to the transverse acceleration αy is found by multiplying the said data vector and the estimated value of a parameter vector. While using an estimation algorithm, the estimate of the parameter vector is calculated from the estimate detected before and an error, and a state vector is found by multiplying the matrix of data vectors and the matrix of parameter vectors. Thus, a yawing velocity (w) and a transverse velocity Vz are extracted.