PROBLEM TO BE SOLVED: To develop a novel surface modification agent which can modify a surface of a hydrophobic material, in particular a medical material used in circumstances in which the medical material is in contact with a biological substance, with a convenient means and with a membrane having high safety.SOLUTION: A polymer for surface modification is a polymer for modifying a surface of an inorganic material or an organic material and is a copolymer including: a monomer unit (i) having a phosphorylcholine group on a side chain thereof； a monomer unit (ii) having a hydrophobic group for physical adsorption on the surface of the material on a side chain thereof； and a monomer unit (iii) having a reactive group for cross-linking between chains of the polymer for surface modification and for chemical adsorption on the surface of the material on a side chain thereof.
