PURPOSE: To obtain a compact sensor having a relatively long life, by changing the amount of light passing optical fiber by utilizing resonance and vibration of a vibrating plate, on which a voltage to be measured is applied, and detecting the voltage to be measured with said amount of light.

CONSTITUTION: A vibrating plate 1 is constituted by bimorph type piezoelectric ceramics. The vibrating plate 1 is supported by a fixing stage 3 in a cantilever manner. When a voltage to be measured Vin is applied to the vibrating plate 1 through a capacitor C, the vibrating plate 1 is resonated and vibrated stably in synchronization with the voltage to be measured. A light screening plate 4, which is attached to the vibrating plate 1, is moved up and down accompanied by the resonance and vibration of the vibrating plate 1. As a result, a light transmission path between an input optical fiber 6 and an output optical fiber 7 is intermittently screened. Therefore, a photodetector, which is provided at one end of the fiber 7, outputs the detected signal. The amount of the emitted light is found based on the output light of the photodetector. Thus not only the presence or absence of the voltage to be measured but also the voltage value can be detected. In this way, the compact sensor also characterized by a relatively long life can be obtained.