By slowing down the passing velocity of a DNA molecule in a nanopore, the accuracy of the reading of a nucleotide sequence of DNA is improved. A small temperature difference is introduced between a DNA molecule having an asymmetric and periodic structure and a nanopore membrane that carries the DNA molecule, whereby the DNA molecule that passes through a nanopore can move in one direction and the passing velocity of the DNA molecule in the nanopore can be controlled and reduced. In this manner, the accuracy of the analysis of a nucleotide sequence can be improved. Furthermore, it becomes possible to dissociate double-stranded DNA into single-stranded DNA molecules by the action of temperature and subject the single-stranded DNA molecules to a measurement selectively. Furthermore, it also becomes possible to select the polarity of a DNA molecule and subject the DNA molecule to a measurement.