PURPOSE: To make lead wires strong and to decrease the adverse effect of the lead wires on the filter characteristics, by taking out the lead wires connecting the mechanical system and the electric circuit from a vibrating node at the center in the lengthwise direction of a converter.

CONSTITUTION: Two converters 13 and 14 of Langevin type primary oscillation mode and three resonators 15, in which a piezoelectric porcelain plate D is bonded between two constant elastic metallic rods B and C of different length are welded with supporting lead wires 17∼21 for the lengthwise center vibrating node in parallel, and the vibrating node opposite to the supporting lead wires is fixed with molding and independently welded to a metallic fixture of a supporting base 27 provided with electrically insulated supporting metallic fixtures 24∼26. Further, couplers 22 and 23 to the converters 13 and 14 between the converters 13 and 14 and the resonator 15 are welded to the metallic rod B electrically insulated with supporting lead wires 18 and 19 via the plate D. The supporting lead wires 18∼21 of a mechanical filter thus assembled are cut off at four parts as shown in the mark A, allowing to use the supporting lead wires 18 and 19 of the part C as input and output terminals.