A resist underlayer film for lithography does not cause intermixing with a resist layer, has high dry etching resistance and high heat resistance, and generates a low amount of sublimate. A resist underlayer film-forming composition containing a polymer having a unit structure of the following formula (1): wherein A is a divalent group having at least two amino groups, the group is derived from a compound having a condensed ring structure and an aromatic group for substituting a hydrogen atom on the condensed ring, and B1 and B2 are each independently a hydrogen atom, an alkyl group, a benzene ring group, a condensed ring group, or a combination thereof, or B1 and B2 optionally form a ring with a carbon atom bonded to B1 and B.