PURPOSE: To easily discriminate the voltage signal due to an input elastic wave without being effected by external noise by mounting an absorbing body whose acoustic impedance is almost equal to that of a piezoelectric element on the detection surface of the piezoelectric element through an electrode.
CONSTITUTION: An absorbing body 14 whose acoustic impedance is almost equal to that of a piezoelectric element 11 is bonded to the under surface of the piezoelectric element 11 through an electrode 13. The elastic wave from a sample is inputted to the piezoelectric element 11 through input electrodes 18, 12 and converted to a voltage signal by the element 11 to be outputted through the electrode 13, a tin foil 19, a take-out electrode 15 and a lead wire 21. The elastic wave reaching the electrode 13 is attenuated by the absorbing body 14 without being reflected. By this method, a pulse like signal receiving no effect of the reflected wave and faithfully reflecting the waveform of the elastic wave is obtained. Therefore, the discrimination from external noise becomes easy.