A positive working resist composition comprising (A1) a resin containing a repeating unit represented by formula (1) defined in the specification and a repeating unit represented by formula (2) defined in the specification and having a property of being insoluble or sparingly soluble in an alkali developing solution and becoming soluble in an alkali developing solution by the action of an acid, and (B) a compound capable of generating sulfonic acid upon irradiation with active rays or radiations in an amount of from 5 to 20% by weight based on the total solid content of the positive working resist composition.