JP2542065B

PURPOSE:To prevent malfunction due to an unnecessary reflected signal by converging light which is emitted by another vehicle on a light spot position detecting means by a converging means such as a condenser lens. CONSTITUTION:If a leading vehicle 24 is, for example, at a left-side position shown by a broken line, infrared rays 26 emitted from its exhaust pipe 24a passes through an optical path shown by a broken line and is converted on a right-side photodetection body 28. In this state, the leading vehicle 24 moves to the right side, the light passes an optical path shown by a solid line in a figure and is converged on a left-side photodetection body 28b, and the light spot is positioned on the left-side photodetection body 28b. When the leading vehicle moves to the left side, the light spot shifts in position to the right. Here, the movement direction and movement quantity of the light spot 32 are found to obtain the movement direction and movement quantity of the leading vehicle 24. Thus, the movement direction and quantity of the leading vehicle 24 are detected and the direction of the visual field 34 of a vehicle-to-vehicle distance detecting means 2 is controlled. Consequently, a reflected signal is only a signal which is reflected by the leading vehicle at all times and malfunction which is caused by an unnecessary reflected signal is evaded.