Zwitterionic monomers are molecules that have a cationic moiety and an anionic moiety in the same molecule. Zwitterionic monomers are mainly known as phosphorylcholine, sulfobetaine, and carboxybetaine, and polymers derived from each monomer are known to exhibit high hydrophilicity and to have a protein nonspecific adsorption control ability comparable to that of PEG. Therefore, these polymers are applied to medical devices such as stents and catheters, hydrogels, and drug delivery systems.