Disclosed is an emulsifier comprising, as an active ingredient, a polyfluoroalkylphosphonic acid salt represented by the general formula: CnF2n+1(CH2CF2)a(CF2CF2)b(CH2CH2)cP(O)(OM1)(OM2), wherein M′ is a hydrogen atom, an alkali metal, an ammonium base, or an organic amine base, M2 is an alkali metal, an ammonium base, or an organic amine base, n is an integer of 1 to 6, a is an integer of 1 to 4, b is an integer of 1 to 3, and c is an integer of 1 to 3. An aqueous solution or organic solvent solution of the emulsifier can be effectively used to emulsify a perfluoropolyether oil or a perfluorocarbon compound. The resulting emulsion exhibits excellent emulsification stability, and thus can be effectively used as a mold-releasing agent.
