PURPOSE: To simplify the structure of a detector, by utilizing the resonance of a cantilever for a resonator, and using ordinary products for parts.

CONSTITUTION: A resonator 20, which is a cantilever that is resonated at an arbitrary vibrating frequency, and a piezoelectric element 19 are compressed and fixed to one side of a base 12. An electric signal is taken out of the piezoelectric element 19. A terminal table 10 also tightens the resonator 20 and the piezoelectric element 19. A connector 17 is formed on the other side of the base 12. The base 12 is fixed to a vibrating body. When the resonator 20 is resonated by the vibration of the vibrator, only the vibration having the resonant frequency of the resonator 20 among the resonant frequencies of the vibrator is amplified by the resonator 20 and a weight 9. The vibration is applied to the piezoelectric element 19 and converted into an electric output. Thus the resonant frequency can be readily selected. By the structure wherein the detector is embedded in the vibrator, machining becomes easy and the price becomes very low.