PURPOSE: To improve heat resistance and moisture resistance by forming a guide groove layer on a substrate by using a resin curable by UV rays consisting of a monomer compsn. contg. a specific compd. as a photopolymerizable prepolymer and a photopolymerizable monomer.

CONSTITUTION: The guide groove layer is formed on the substrate by using the resin curable by UV rays having the polyester methacrylate expressed by the formula I at 50W80wt% and the epoxy acrylate expressed by the formula II at 5W35wt% as the photopolymerizable prepolymer and dipentaerithritol hexacrylate (DPHA) as the photopolymerizable monomer at ≥5wt% and ≤30wt% as the monomer compsn. The DPHA is a hexafunctional photopolymerizable monomer and has high reactivity and crosslinkability and therefore, said monomer forms three-dimensional crosslinking in the stage of curing by UV rays and has the much higher glass transition temp. The heat resistance and moisture resistance are thereby remarkably improved.