An object to be achieved by the present invention is to provide a nucleic acid amplification method by which a nucleic acid can be amplified substantially isothermally using oligonucleotide primers and DNA polymerase capable of strand displacement. The present invention provides a nucleic acid amplification method which comprises performing substantially isothermal incubation of a reaction solution containing at least one type of deoxynucleotide triphosphate, at least one type of DNA polymerase having strand displacement activity, a divalent cation, at least 0.01% or more surfactant, at least two types of oligonucleotide primer, and the nucleic acid fragment as a template so as to perform a polymerase reaction that initiates from the 3′ end of the primer and thus amplifying the nucleic acid fragment.