PURPOSE: To form an optical voltage sensor excellent free from the effect of double refraction temperature characteristic of a wavelength plate in a smaller size with limited components by arranging a polarizer, a wavelength plate, an electrooptical element and an analyzer.

CONSTITUTION: Two polarizers 21a and 21b and electrooptical elements 23a and 23b are employed as polarizer and electrooptical element while a pair of wavelength plates 22a and 22b is employed to produce values of optical phase differences imparted to incoming light as such as the same value opposite to each other, positive or negative. A first wavelength plate 22a, a first electrooptical element 23a, a second polarizer 21b, a second wavelength plate 22b and a second electrooptical element 23b are arranged between the first polarizer 21a and the analyzer 24 to allow the ignoring the effect of double refraction temperature characteristic of the wavelength plate thereby achieving higher measuring accuracy.