A positive resist composition for forming a thick-film resist having a film thickness of 1 to 15 μm, the composition comprising: a resin component (A) that includes a polymer compound (A1), which has a weight average molecular weight of 20,000 to 50,000, and includes a structural unit (a1) derived from a hydroxystyrene and a structural unit (a2) derived from an acrylate ester containing an acid dissociable, dissolution inhibiting group, an acid generator component (B) that generates acid upon exposure and includes an onium salt-based acid generator having an anion moiety represented by general formula (I): R4″SO3− (wherein, R4″ represents a linear or branched alkyl group or fluoroalkyl group of 4 carbon atoms), and a nitrogen-containing organic compound (D) that includes a tertiary aliphatic amine.