To provide a contact lens material having not only high oxygen permeability but also high wettability.

This new class compound is usable as a new cross-linking agent for a hydrophilic monomers containing an acrylic, a vinyl and/or a styrene for preparing a new UV-curable hydrophilic copolymer suitable for a biomedical article, especially a contact lens. The new cross-linking agent can polymerize a hydrogel system containing both of at least one kind of vinyl, and at least one kind of styrene or acrylic group in a monomer mixture.