An elastic diaphragm (110) is divided into multiple elastic vibration regions (112) by slits (111) of a prescribed shape. Piezoelectric vibrators (120) mounted individually on at least some of the multiple elastic vibration regions (112) of said elastic diaphragm (110) are stretch-vibrated by applying an electric field. For that reason, the elastic vibration regions (112) of the one elastic diaphragm (110) can by vibrated individually by means of the multiple piezoelectric vibrators (120). Consequently, the peak value of the vibration frequency can be freely adjusted for each elastic vibration region.