Provided is a positive photoresist composition containing, as an essential component, a novolac phenolic resin (C) prepared by condensing an aromatic compound (A) represented by general formula (1) or (2) with an aliphatic aldehyde (B). This positive photoresist composition has high sensitivity and high heat resistance at the same time, and is suitable for use as a positive photoresist in, for example, the manufacture of semiconductor devices such as ICs and LSIs, the manufacture of displays such as LCDs, and the manufacture of printing plates. (In the formulas, R1, R2, and R3 are each independently an alkyl group having 1 to 8 carbon atoms; m, n, and p are each independently an integer of 0 to 4; q is an integer of 1 to (5−p); and s is an integer of 1 to (9−p).)