To use a lane marker to measure the vehicle behavior such as the deviation in the transverse direction, the attitude, and the speed of a vehicle.

The lane marker is arranged in the center of road along the road. Two lane marker detection means which magnetically, electrically, or optically detect the lane marker are provided in each of the front and the rear of the vehicle. The transverse deviation as the extent of movement in the transverse direction of the vehicle to the road center, the attitude of the vehicle to the road direction and the speed relative to the ground of the vehicle are obtained based on the sum and differences of outputs of four lane marker detection means obtained at the time of lane marker detection. The lane marker is used to accurately obtain the deviation in the transverse direction of the vehicle, the attitude of the vehicle, and the speed relative to the ground of the vehicle without independently providing a sensor like a camera.