To securely detect a marker when the marker is arranged near a stop lamp in a system where the marker of a preceding vehicle is detected.

A preceding vehicle detection sensor 10 is loaded on a self- vehicle and a marker 20 installed at the rear part of a preceding vehicle 200 is detected. When the marker 20 is arranged near the stop lamp, the stop lamp is connected with the marker on luminance by the lighting of the stop lamp. Nevertheless, the marker and the stop lamp are distinguished from each other based on the position relation of the marker and the shape of the marker. Thus, the lighting of the stop lamp of the preceding vehicle can be detected through distinguishing the marker and the stop lamp.