PURPOSE: To enable the accurate positioning of piezoelectric elements by providing the piezoelectric elements, which abut on a power supply member, with positioning means, which regulate the positions inside the planes perpendicular to the axial direction of an elastic body.

CONSTITUTION: For piezoelectric element plates 30 and 40, which are stacked with a power supply member (electrode plate) 50 between, electrodes a and b are made on both sides of the diameter part on each surface side, and small diameters of through holes 31 and 41 in pairs are formed, for example, axisymmetrically in the insulating parts d at the diameter parts, which are recessed by the amounts of thicknesses of the electrodes a and b. Moreover, each through hole of the piezoelectric element plates 30 and 40 engages with the projections 51 and 52 of the electrode plate 50, and the piezoelectric element plates 30 and 40 on both sides of the electrode plate 50 are laminated, being positioned to have the positional phases of 90° around the axis. Hereby, the piezoelectric element plates 30 and 40 can be positioned in the specified positions.