A chemical amplification type positive resist composition is provided, comprising a resin which has at least one polymerization unit selected from a polymerization unit of 3-hydroxy-1-adamantyl acrylate and a polymerization unit of 3,5-dihydroxy-1-adamantyl (meth)acrylate, a polymerization unit of hydroxystyrene and a polymerization unit having a group uhstable to an acid, is itself insoluble or poorly soluble in an alkali but becomes alkali-soluble after said group unstable to an acid is dissociated by the action of an acid; and an acid generator, the composition being excellent in various abilities such as sensitivity, resolution, heat resistance, film retention ratio, applicability, exposure clearance, dry etching resistance and the like, particularly having further improved resolution and exposure clearance.