PURPOSE: To enable the effective development of the transmitting and receiving function performed by the same sensor, by simple and small constitution such that the impedance matching at the time of the transmission and reception of ultrasonic waves is controlled by a transistor, a diode and a resistor.

CONSTITUTION: When an ultrasonic wave transmitting order signal and the pulse signal coincided with the resonance frequency of an ultrasonic sensor 1 are respectively supplied to input terminals 15, 23, an NPN transistor 17 and a PNP transistor 20 are turned ON while an NPN transistor 25 is turned ON and OFF, and the signal from a power source 2 is supplied to the sensor 1 in a low impedance state through the transistor 20, a diode 21, a resistor 22 and a condenser 27 to perform the transmission of ultrasonic waves while impedance becomes infinite by the perfect interruption of the transistors 25, 20, the diode 21 and the condenser 27 being turned OFF at the time when ultrasonic waves are received by the sensor 1. By this mechanism, impedance matching is controlled by simple and small constitution requiring no pulse transformer and the transmitting and receiving functions by the same sensor is effectively developed.