PURPOSE: To improve practical use by making alarm display even if there is no object in a detection area after an alarm is displayed and providing a means that halts the continuation of the alarm display using damping operation.

CONSTITUTION: When there is an object 4 is a detection area 5, the program presses through steps 9108, 9109, and 9112. Consequently, an alarm is displayed by a buzzer 7 and is continued. Then once the alarm has been continued, since the program always passes through the steps 9108, 9110, and 9112 even if there is the object 4 in the detection area 5, the alarm is continued. Subsequently, when there is no object 4 in the detection area 5 and a brake is actuated, since the program passes through the steps 9108, 9110, 9111, and 9112, the alarm is halted. As a result, when a driver damps and actuates the brake, the continuation of the alarm is arbitrarily halted and a control circuit 9 is restored to the operating status just after feeding is started.