PURPOSE: To attain a simple structure, high light utilization rate, low electric power consumption, low cost, etc., by successively laminating a first transparent electrode, transparent electrolyte, optical semiconductor and second transparent electrode.

CONSTITUTION: This spatial optical modulator is constituted by successively laminating the first transparent electrode ITO, the transparent electrolyte C2H5OH, the optical semiconductor a-WO3 and the second transparent electrode ITO. Image patterns are written by the intake of ions into the optical semiconductor a-WO3 from the transparent electrolyte C2H5OH when the modulator is irradiated with light having the energy gap larger than the band gap of the optical semiconductor a-WO3 as modulation input from the first electrode ITO side or the intake of the ions from the optical semiconductor a-WO3 into the transparent electrolyte C2H5OH or the release of the ions from the optical semiconductor a-WO3 to the transparent electrolyte C2H5OH. The image patterns are read out by the light having the energy smaller than the band gap of the optical semiconductor a-WO3. Further, the image patterns are erased by impressing a specific voltage between the first transparent electrode ITO and the optical semiconductor a-WO3 or the second electrode ITO after writing of the image patterns.