Hydrophilic coating agent

A hydrophilic coating agent for forming a film having hydrophilicity, comprising an alkoxysilyl group-containing polymer prepared by polymerizing a monomer component comprising a betaine monomer and an alkoxysilyl group-containing compound, wherein the alkoxysilyl group-containing compound is an alkoxysilyl group-containing compound represented by the formula (IV):

• wherein each of R17, R18 and R19 is independently an alkyl group having 1 to 4 carbon atoms or an alkoxy group having 1 to 4 carbon atoms, and at least one of R17, R18 and R19 is an alkoxy group having 1 to 4 carbon atoms, and R20 is an alkylene group having 1 to 12 carbon atoms;
• an azobis(trialkoxysilyl) compound represented by the formula (V):
• wherein each of R22 to R27 is independently an alkyl group having 1 to 4 carbon atoms or an alkoxy group having 1 to 4 carbon atoms, and at least one of R22 to R27 is an alkoxy group having 1 to 4 carbon atoms, and each of R28 and R29 is independently an alkylene group having 1 to 12 carbon atoms, and one or two methylene groups included in the alkylene group can be substituted with —O— group, —C(O)O— group, —O(O)C— group, —NH— group, —CO— group, an arylene group, urethane bond or 1,2-imidazoline group, 2,2′-azobis[2-(1-(triethoxysilylpropylcarbamoyl)-2-imidazoline-2-yl)propane];
• or 2,2′-azobis[N-[2-(triethoxysilylpropylcarbamoyl)ethyl]isobutylamide].