PURPOSE: To detect a relative position relation to a preceding vehicle properly, and achieve a smooth acceleration/deceleration control by determining an existence probability based on a deflection quantity obtained by CCD sensors, and evaluating a relative position to a vehicle based on a danger degree.

CONSTITUTION: Pairs of CCD sensors 1a, 1b... disposed apart from each other are provided horizontally to detect an image of a preceding vehicle. A detection output is converted into a digital signal to be inputted to a microcomputer 24. The microcomputer 24 calculates a bit shift n1 where a correlation degree becomes the minumum for every azimuth θ to determine a bit shift quantity n1(θ). Next, an existence probability (rθ) is determined based on the correlation degree and an inclination. In the meanwhile, a danger degree Cr(rθ) having a property of inverse proportion to the azimuth and a distance (r) from a vehicle is set as a function of a predetermined zone in front of the vehicle, and by double integration of a product of these, an evaluation function F is calculated. A demand acceleration is calculated based on the evaluation function F for performing operation control.