A method and apparatus for amplifying nucleic acids. The method includes introducing into a reaction vessel via different inlet channels a reactant aqueous solution containing reactants for nucleic acid amplification and a fluid that is phase-separated from the reactant aqueous solution and does not participate in amplification reaction, creating a plurality of reactant aqueous solution droplets surrounded by the fluid by contacting the reactant aqueous solution with the fluid in the reaction vessel, and amplifying the nucleic acids in the reactant aqueous solution droplets. The apparatus includes a substrate, a reaction vessel formed inside of the substrate, at least one first inlet channel formed inside the substrate, connected to an end of the reaction vessel, and allowing introduction of a reactant aqueous solution containing reactants for nucleic acid amplification into the reaction vessel, a second inlet channel formed inside the substrate, connected to the end of the reaction vessel, and allowing introduction of a fluid that is phase-separated from the reactant aqueous solution and does not participate in amplification reaction into the reaction vessel, and a heating unit installed on the substrate in such a way to thermally contact with the substrate and heating the substrate.