A pattern forming method includes forming a first organic film by coating an etching target film with a composition including a polymer including a cross-linkable component, infiltrating an inorganic substance into the first organic film, cross-linking the polymer, forming a second organic film on the first organic film, forming a second organic film pattern by patterning the second organic film, forming a first organic film pattern having a pitch reduced to one-half of a pitch of the second organic film pattern by patterning the first organic film by a self-aligned patterning method that uses the second organic film pattern as a core pattern, forming an etching target film pattern having a pitch reduced to one-half of a pitch of the first organic film pattern by patterning the etching target film by a self-aligned patterning method that uses the first organic film pattern as a core pattern.