To provide a multiplex method of nucleic acid amplification, suitable for conducting a reaction of many nucleic acids desired to amplify in a mixed state as a homogeneous ambience.

The multiplex method of nucleic acid amplification by a PCR amplification process includes using primers each 32 bases or more in length, making an annealing at a temperature lower than the respective Tms of the primers, and conducting an extension reaction for 1-10 min, i.e. annealing/extension reaction for a long period of time enough to accomplish the aimed uniform nucleic acid amplification by the respective primers.