[Problem] Provided are: a pattern forming method by which a pattern can be formed by development using a thermosetting resin composition and a cured layer having excellent curability can be obtained; a thermosetting resin composition used in the pattern forming method; and a printed circuit board.[Means for Solution] The pattern forming method according to the present invention is characterized by comprising the steps of: (A) forming a resin layer composed of an alkali-developable thermosetting resin composition comprising a photobase generator on a substrate; (B) activating the photobase generator contained in the alkali-developable thermosetting resin composition by irradiation with a light in a pattern form so as to cure an irradiated part; and (C) forming a negatively patterned layer by removing a non-irradiated part by alkali development.