A positive resist composition including a resin component (A) which exhibits increased alkali solubility under action of acid and an acid-generator component (B) which generates acid upon exposure, the resin component (A) including a structural unit (a1) represented by general formula (I) shown below: wherein R represents a hydrogen atom, a halogen atom, a lower alkyl group or a halogenated lower alkyl group; R1′ represents a hydrogen atom or a lower alkyl group; n represents an integer of 0 to 3; R1 represents a lower alkyl group, a fluorine atom, or a fluorinated lower alkyl group; and p represents an integer of 0 to 2.