PURPOSE: To use the inexpensive A/D convertor having low sampling frequency by setting up a vibration gyroscope at the part on the vehicle receiving a gentle angular velocity change at the vehicle turning time.
CONSTITUTION: A vibration gyroscope 21 is set up at the vicinity of the intersection between the center line l 1 and rear wheel axial line l 2 in the running direction of an automobile 20. In case of the automobile 20 turning at a cross the locus of the rear wheel 20b becomes simple close to the actual road condition against the complicated locus of the front wheel 20a. The part close to the wheel 20b receives a gentle change in the angular velocity therefore and the analog electric signal transmitted from the gyro 21 which is fitted thereto becomes changing slowly. Consequently, the arithmetic result of the necessary accuracy is obtd. even by the inexpensive A/D convertor having small sampling frequency and the cost of the device can be reduced.