A new optical switching device based on photochromic dye isomerization in a planar type active waveguide was proposed, The polymeric thin-film composed of a well designed spirooxazine derivative shows new light absorption band in the visible range (lambda (max) = 587 nm) due to very fast photochromism under UV irradiation. Since this polymeric thin-film can also act as an intrinsic waveguide, the output intensity of input and guided visible light (lambda = 633 nm. He-Ne Laser) through planar thin-film was decreased effectively during UV irradiation.