A polymer includes a repeating unit shown by a general formula (1) in which R1 represents a hydrogen atom or a methyl group, R2 represents a substituted or unsubstituted linear or branched monovalent alkyl group having 1 to 20 carbon atoms, an alicyclic group having 3 to 25 carbon atoms, or an aryl group having 6 to 22 carbon atoms, and X represents a substituted or unsubstituted methylene group or a substituted or unsubstituted linear, branched or alicyclic hydrocarbon group having 2 to 25 carbon atoms. The polymer has a polystyrene-reduced weight average molecular weight determined by gel permeation chromatography (GPC) of 3000 to 100,000.