An optical voltage prove includes: an optical modulator 1 having two modulation electrodes 11 and 12, the optical modulator 1 being configured to modulate an intensity of an incident light depending on a voltage between the two modulation electrodes and output the incident light which is modulated; an input/output optical fiber 2 connected with the optical modulator 1; two contact terminal attachment portions 5, 6 to which contact terminals 3, 4 can be detachably attached and contacted, the two contact terminals 3, 4 being configured to be in contact with the points to be measured, the two contact terminal attachment portions 5, 6 being respectively connected with the modulation electrodes 11, 12; and a package 8 that houses the optical modulator 1 and a part of the input/output optical fiber 2. A voltage signal induced via the contact terminals 3, 4 is converted into an optical intensity modulation signal. When an electric wave having a measurement frequency is applied while the contact terminal attachment portions 5, 6 are opened, the package 8 exhibits a shielding effect of attenuating the electric wave by 15 dB or more compared to an output signal intensity measured without providing the package.