A fluorine-containing novolac resin represented by the following formula, as well as a fluorine based surfactant and a fluorine based surfactant composition, which include the fluorine-containing novolac resin. In the formula, R represents a fluorinated alkyl-containing substituent, R′ represents a hydrogen atom or a methyl group, R″ represents a hydrogen atom or a non-fluorinated substituent, —X— represents any one of following four types of linking groups, —X′ represents any one of three following types of substituents, n represents 0 or an integer of 1 or more, m represents an integer of 1 or more, and n+m is an integer of 2 or more.