A resist underlayer film that exhibits removability and preferably solubility only in wet etching reagent solutions, while exhibiting good resistance to resist developers that are resist solvents or aqueous alkali solutions. The composition for forming a resist underlayer film includes a dicyanostyryl group-bearing polymer (P) or dicyanostyryl group-bearing compound (C) and includes solvent, and does not contain a protonic acid curing catalyst and does not contain an alkylated aminoplast crosslinking agent derived from melamine, urea, benzoguanamine, or glycoluril.