A positive type resin composition comprising (A) a resin component comprising within the principal chain a structural unit derived from a (meth)acrylate ester and incorporating an acid dissociable, dissolution inhibiting group containing a polycyclic group on an ester side chain section, for which the solubility in alkali increases under the action of acid, (B) an acid generator component which generates acid on exposure, and (C) an organic solvent, wherein the component (A) comprises both a structural unit derived from a methacrylate ester and a structural unit derived from an acrylate ester. According to such a resist composition, a resist pattern can be formed which displays little surface roughness and line edge roughness on etching, and also offers excellent resolution and a wide depth of focus range.