The present invention provides a chemical amplification type positive photoresist composition which is excellent in storage stability as a resist solution in a bottle. A novolak resin or a hydroxystyrenic resin is reacted with a crosslinking agent to give a slightly alkali-soluble or alkali-insoluble resin having such a property that solubility in an aqueous alkali solution is enhanced in the presence of an acid, which is then dissolved in an organic solvent, together with (B) a compound generating an acid under irradiation with radiation to obtain a chemical amplification type positive photoresist composition wherein the content of an acid component is 10 ppm or less.