To provide an analytical device capable of detecting polynucleotide even at a very low concentration thereof and of rapidly giving analytical results.

Disclosed is a method for amplifying a polynucleotide in a sample by conducting a polynucleotide amplification reaction, wherein the method comprises a step of providing a device with a solid substrate which is formed to include at least one polynucleotide amplification reaction chamber having at least one mesoscale cross-sectional dimension of 0.1 to 1,000 μm and comprising at least one reagent required for in vitro amplification of the polynucleotide and a step of providing a device comprising at least one port communicated to the reaction chamber for introducing the reagent into the reaction chamber. The method also comprises a step of introducing, into the reaction chamber through the port, liquid comprising a polynucleotide sample, at least one reagent for amplification of the polynucleotide sample in the chamber, and a blocking agent.