To introduce a biomolecule into a nanopore without the need to check the position of the nanopore in a thin film. In addition, displacement stability is ensured and stable acquisition of blocking signals is realized. An immobilization member 107 having a larger size than a thin film 113 with a nanopore 112 is used, and biomolecules are immobilized on the biomolecule immobilization member 107 at a density that allows at least one biomolecule 108 to enter an electric field region around the nanopore when the biomolecule immobilization member 107 has moved close to a nanopore device 101.