PURPOSE: To achieve a higher detection accuracy in a low frequency range, by fastening two thin piezoelectric elements on both sides of a metal sheet in such a manner the polarizing directions of the piezoelectric elements are the same separately with respect to the direction of applying a kinetic value to make an electric connection in parallel.

CONSTITUTION: Two piezoelectric elements 21 and 22 fastened on both sides of a metal sheet 20 have thin electrode 23W26 formed on the respective surfaces thereof. A lead wire fetching a signal from a piezoelectric diaphragm 100 provides an electric connection between outside electrodes 23 and 24. Here, a total of three lead wires-the lead wire 27, a lead wire 29 to introduce an electric charge generated in the electrodes 23 and 24 to a detection circuit and a lead wire 28 to introduce an electric charge generated in the adhesion side electrodes 25 and 26 to the detection circuit-are arranged. The elements 21 and 22 are fastened on both sides of the sheet 20 in such directions that the polarizing directions of the elements 21 and 22 are the same with respect to the direction of applying a kinetic value. The elements 21 and 22 are con nected electrically in parallel and output thereof are outputted at an output terminals 34 through an operational amplifier 33.