PURPOSE: To prevent at a low cost interference between the sensors that occurs in a sensor system in which a plurality of ultrasonic sensors are laid in line.

CONSTITUTION: Each of a plurality of ultrasonic sensors 1A is provided with an interface circuit 19A which switches the transmitting/receiving motions of the ultrasonic sensor into 'off operating' in conformity to the motion control signal DA which is fed externally. The interface circuit of each ultrasonic sensor is so arranged as to be fed, as motion control signal DA, with the sensing signals SA of the other sensors via an OR circuit 30A consisting of a plurality of diodes.