PURPOSE: To obtain sufficient output acoustic pressure in a wide frquency band, by linking the piezo-vibrator, which is the sound source, and the diaphragm thrugh a cylindrical linkage material, in the ultra-thin piezo-electric speaker which has a good frequency characteristic and is the most suitable for the portable radio and so on.

CONSTITUTION: The vibration amplitude of piezo-vibrator 20 is transferred to diaphragm 40 through cylindrical linkage material 60, and sound is generated by vibration of this diaphragm 40. Though the vibration amplitude is transferred to diaphragm 40 with a low efficiency in comparison with linking with the diaphragm in the center of piezo-vibrator 30 only when vibrator 20 vibvates the main resonance mode, the vibration amplitude is transferred to diaphragm 40 effectively when vibrator 20 vibrates in the sub-resonance mode other than the main resonance mode. As a result, sufficient acoustic pressure can be obtained in the wide frquency band from the middle and low frequency band to the high frequency band.