Abstract: The tip (26a) of a rear-end mount (26) that fastens the piezoelectric element (6) is tapered. The rearmost part (26b) of the rear-end mount (26) that fastens the piezoelectric element (6) is indented in a U shape. An eccentric pin (30), which extends in the direction perpendicular to the longitudinal direction of the piezoelectric element (6), is fitted in this indentation. The rear-end mount (42), which fastens one end of the finger (8), is provided with a pin (46) that extends in the direction perpendicular to the longitudinal direction of the piezoelectric element (6). This pin (46) is provided with a spiral groove (48) over practically its entire length.