PURPOSE:To reduce the number of transmitting/receiving circuits and the number of signal lines by providing a variable resistor means controlling the passage of the received signal and controlled with its internal resistance value by the control signal, a passing signal selecting means connected in parallel with the variable resistor means, and an opening control means in the thickness direction made of fixed impedance inserted between the junction of both means and the ground. CONSTITUTION:The transmitted signal of a transmitting circuit 4A excites vibrators 11A and 11B via a high-voltage passing diode circuit 13 and directly excites a vibrator 12, ultrasonic waves are concurrently transmitted from three vibrators in the thickness direction. Among the reflected signals returned from an object to the vibrators 11A, 11B and 12, the signal received by the vibrator 12 enters a receiving circuit 4B, the signals received by the vibrators 11A and 11B enter an FET 14. The received signals are weak and can not pass the high-voltage passing diode circuit 13, only the received signal of the center vibrator 12 is inputted to the receiving circuit 4B. The opening value in the thickness direction of a probe 1 can be controlled.
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