The present invention provides a chemical amplification type positive resist composition comprising (A) a resin which comprises (i) 5 to 50% by mol of a structural unit of the formula (I), (ii) 5 to 50% by mol of a structural unit of the formula (II) and (iii) 5 to 50% by mol of at least one selected from the group consisting of structural units of the formulas (III) and (IV), and (B) an acid generator. The present composition is suitable for excimer laser lithography using ArF, KrF and the like, and shows various outstanding resist abilities, specifically, gives better effective sensitivity and resolution to resist patterns obtained therefrom, and gives particularly excellent pattern shape and excellent line edge roughness. ##STR00001##