PURPOSE: To effectively prevent a drop of photosensitivity, by obtaining a liquid crystal photosensitive device which has an optical modulation function in a modulation wavelength area where a polarizing plate has a polarizing characteristic, and also whose modulation wavelength area contains all wavelength areas where a wavelength generated by a light source optical system part, and a photosensitive wavelength area of a photosensitive part are overlaped.

CONSTITUTION: A light source 20 and a liquid crystal optical modulation part 21 for constituting a liquid crystal optical signal generating part are shown in the figure, and the liquid crystal optical modulation part 21 consists of polarizing plates 25, 26, a liquid crystal panel 23 and a liquid crystal driving part 24. Light 27 emitted from the light source 20 is modulated by the liquid crystal optical modulation part 21, becomes modulated light 28, and is irradiated to a photosensitive part 22. Also, a light source optical system part is constituted by adding a wavelength filter 29, a condensing lens 30 and an image forming lens 31 to said part. As for the image forming lens 31, an erecting image of 1:1 can be obtained by using a convergent optical fiber array.