Polymer compound, positive resist composition and method of forming resist pattern

A positive resist composition, comprising a resin component (A) that exhibits increased solubility in an alkali developing solution under action of acid, and an acid generator component (B) that generates acid upon exposure, wherein

• said resin component (A) comprises a polymer compound (A1) having a structural unit (a0) represented by a general formula (a0-1) shown below, and a structural unit (a1) that is derived from an acrylate ester containing an acid dissociable, dissolution inhibiting group but is not classified as said structural unit (a0):
• [wherein, R represents a hydrogen atom, a lower alkyl group, or a halogenated lower alkyl group;
• A represents a divalent aliphatic cyclic group that may have a substituent;
• B represents a divalent hydrocarbon group that may have a substituent;
• r represents an integer of 1;
• and R1 represents an acid dissociable, dissolution inhibiting group].