A resist underlayer film-forming composition capable of providing a resist underlayer film exerting a sufficient anti-reflection function particularly in a KrF process, a high solvent resistance and a high dry etching speed, and enables the formation of a photoresist pattern having a good cross-sectional shape. The composition includes a copolymer containing: structural unit (A) derived from a diepoxy compound; and structural unit (B) derived from a compound represented by formula (1) [wherein: A represents a benzene or cyclohexane ring; X represents a hydrogen atom, alkyl or alkoxy group having 1 to 10 carbon atoms and optionally substituted by a halogen atom, or an alkoxycarbonyl group having 2 to 11 carbon atoms; and Y represents —COOH or -L-NHCO—Z—COOH (wherein: Z represents an alkylene group having 3 to 10 carbon atoms and optionally substituted by an oxygen atom, sulfur atom or nitrogen atom; and L represents a single bond or a spacer)].