Provided is a resist copolymer which has favorable sensitivity, enables a resist pattern to be formed to have a favorable shape, has favorable dry etching resistance when a dry etching is carried out using the resist pattern as a mask, and suppresses the surface roughness of a pattern formed by carrying out a dry etching process to a substrate.A resist copolymer including a constituent unit (1) based on a (meth)acrylic acid ester derivative having a cyclic hydrocarbon group such as an adamantane ring and two or more cyano groups bonded to the cyclic hydrocarbon group, a constituent unit (2) having a lactone backbone and a cross-linking cyclic structure, and a constituent unit (3) having an acid leaving group.