To obtain a photoresist polymer which is capable of dissolving easily and surely into a solvent at the time of preparing a photoresist resin composition.

The photoresist polymer has at least one kind of a repeating unit selected from among (A) a repeating unit containing a lactone skeleton, (B) a repeating unit containing a group to be eliminated by an acid and to become alkali soluble and (C) a repeating unit containing an alicyclic skeleton having a hydroxyl group, and is characterized in that an insoluble matter is 1 wt.% or less when 1 g of the sample is stirred at 25°C for 24 hours into the dissolution in 4 g of propylene glycol monomethyl ether acetate.