A means for increasing development velocity of a positive photoresist composition is provided which contains a photosensitive novolak resin formed by replacing some hydrogen atoms within those of all phenolic hydroxyl groups of alkali soluble novolak resin by 1,2-naphthoquinonediazide sulfonyl group. This means is positive photoresist composition and a formation method of a resist pattern using the composition which contains (A) a photosensitive novolak resin formed by replacing some hydrogen atoms within those of all phenolic hydroxyl groups of alkali soluble novolak resin by 1,2-naphthoquinonediazide sulfonyl group, which is dissolved in (B) propylene glycol alkyl ether acetate.