PURPOSE: To increase the sensitivity to light in a longer wavelength region by using a dye compsn. consisting of a material which enables radical addition polymn., a dye which can be reduced by light, and a thiol to give photosensitivity to the compsn.

CONSTITUTION: This photopolymerizable compsn. consists of a material which enables radical polymn. such as an ethylenic unsatd. compd., a dye which can be reduced by light, and a thiol, and the compsn. has photosensitivity by the dye. The dye which can be reduced by light is preferably a cyanine dye, carbocyanine dye and hemicyanine dye, and for example, 1,1'-dialkyl-3,3,3',3'- tetramethyl indocarboxyanine chloride can be used. A practical example of the thiol is mercaptobenzoxazole, ethoxymercapto-benzothiazole, mercaptobenzothiazle or 1-phenyl-5-mercapto-tetrazole. Thus, the sensitivity of the compsn. is widened over the visible ray spectrum and an orthochromatic system can be obtd.