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

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

• the base component (A) comprises a polymeric compound (A1) containing a structural unit (a0) represented by the general formula (a0-1) shown below and a structural unit (a3) derived from an acrylate ester which has a polar group-containing aliphatic polycyclic group, wherein the polar group comprises at least one member selected from the group consisting of a hydroxyl group, a cyano group, a carboxyl group, and a hydroxyalkyl group in which at least one hydrogen atom in an alkyl group is substituted with a fluorine atom:
• wherein R1 represents a hydrogen atom, a lower alkyl group, or a halogenated lower alkyl group;
• R5 represents an alkyl group;
• R6 represents a substituent selected from the group consisting of an alkyl group, an alkoxy group, a halogen atom and a halogenated alkyl group;
• and e represents an integer of 0 to 5.