PURPOSE: To provide the new monomer useful for producing a photosensitive resin having a specific ultraviolet rays-sensitive region.

CONSTITUTION: The objective monomer of formula I can be obtained, for example, by dissolving a compound of formula II and formic acid in acetone followed by reaction under reflux. Homopolymerization of this monomer or copolymerization of this monomer with another conventional addition polymerization-type monomer yields a photosensitive resin having a photosensitive region for ultraviolet rays of ≥300nm wavelength. Owing to this photosensitive resin, use of industrially inexpensive emulsion-coated photomasks or those made from soda glass capable of transmitting rays having wavelengths falling in the region of ≥300nm becomes possible.