PURPOSE:To facilitate machining and to reduce the weight by jointing a protrusion part, where protrusions are integrated with an annular board, with the annular base part thereby constituting an annular resilient board and composing the protrusion part of a low density material. CONSTITUTION:An annular resilient board part 101 is composed of a highly rigid material such as metal. A piezoelectric body 102 is adhered to the bottom of the resilient board part 101 thus forming a vibrating section. A protrusion part 103 is formed on the other face of the resilient board part 101. The protrusion part 103 comprises a plurality of protrusions 103a. The protrusion part 103 is composed of a material having lower density than the resilient board part 101. The resilient board part 101, the piezoelectric body 102 and the protrusion part 103 constitute a vibrator 104. Upon application of AC voltages having predetermined phase difference onto two sets of electrodes arranged on the piezoelectric body 101, the piezoelectric body 102 elongates/contracts to perform bending vibration with a period corresponding to half of the wavelength of traveling wave. The protrusions 103a amplitude the bending oscillation and drive a moving body 105 pressure contacting therewith.
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