PURPOSE: To make it possible to obtain a high response speed, by extending a photoconductive thin film to the side of a discrete electrode with the film being screened from light, and grounding the discrete electrode through the extended photoconductive thin film.

CONSTITUTION: A photoconductive thin film 12 is formed on an insulating substrate 11. A common electrode 13 and a discrete electrode 14 are formed so as to face each other from both sides of the photoconductive thin film. The photoconductive thin film 12 is extended to the side of the discrete electrode 14. The discrete electrode 14 is connected to a grounding electrode 15, which is formed on the photo conductive thin film 12 and grounded, by way of the extended photoconductive thin film 12. The photoconductive thin film 12 between the discrete electrode 14 and the grounding electrode 15 is converted with a light screening layer 16. The common electrode 13 and the discrete electrode 14 is comb-shaped toward the other electrode. The comb-shaped parts are arranged in an intermeshed pattern. The current flowing between these electrodes in increased by making the facing width between the electrodes large.