A film forming method includes: a preparation process of preparing a substrate having a surface from which a first film without containing silicon and a second film are exposed; a first film formation process of forming a self-assembled monolayer, which has a fluorine-containing functional group and inhibits formation of a third film containing silicon, on the first film; a second film formation process of forming the third film on the second film; a modification process of decomposing the self-assembled monolayer by plasma using a gas containing hydrogen and nitrogen while maintaining a temperature of the substrate to be 70 degrees C. or lower, so that a side portion of the third film, which is formed in a vicinity of the self-assembled monolayer, is modified into ammonium fluorosilicate by active species contained in the decomposed self-assembled monolayer; and a removal process of removing the ammonium fluorosilicate.