A resist pattern forming method includes: in the following order, (1) a step of forming a film on a substrate by using a positive resist composition; (2) a step of exposing the film; and (4) a step of performing development by using an alkali developer after the exposing, wherein the positive resist composition contains (A) a polymer compound having a repeating unit represented by the following formula (I) as defined in the specification, a thickness of the film formed in the step (1) is from 15 to 40 nm, and an alkali component concentration in the alkali developer is from 0.5 to 1.1 mass %.