A water-absorbing polymer obtained from polymerization of (A) and (B) in aqueous medium wherein (A) is a phosphate-containing (meth)acrylic monomer and/or a salt thereof, and (B) is a monomer having one (meth)acrylic group within the molecule and/or a salt thereof that is different from component (A); and reacting the reaction product of (A) and (B) with (C) an organopolysiloxane having a (meth)acrylic group at both ends.