PURPOSE: To improve the efficiency of a measuring electric field which acts to modulate the intensity of the light passing through an optical waveguide zone and to improve measuring efficiency by using electrodes which are laminated and formed of gold and chromium to a prescribed pattern and are subjected to a heat treatment in an oxygen atmosphere.

CONSTITUTION: The gold and chromium are laminated to the prescribed pattern on the surface of a substrate 10 to form the electrodes 30. The electrodes are thereafter subjected to the prescribed heat treatment to form the electrode reaction layer near the surface of the substrate 10. The electrode reaction layer acts as part of the electrode 30 when the sensor is constituted in the above-mentioned manner. The substrate 10 may be constituted with lithium tantalate. The voltage measuring sensitivity is thus increased and the photoelectric potential sensor having excellent characteristics is realized.