A system adapted to be mounted on a pickup truck for warning the driver of the truck should the front section of a fifth wheel trailer pivotally supported on a hitch secured in the bed of the truck approach a point where there is imminent danger of impact between the front section of the trailer and the back of the cab as the truck and trailer are executing a turn. Accordingly, and have the same optical characteristics. The driver stages are connected in series. , four different current level states that can be determined by the number of holes injected into, e. Then, when the magnetic field is provided to the magnetic substance fixedly holding the SIL which is floating, the movement operation to separate the SIL to the higher position than the height of the foreign material from the information reading surface together with the magnetic substance, is conducted.