Provided are a first tank; a second tank; a thin film having a nanopore, which communicates the first tank to the second tank, and disposed between the first and second tanks; a first electrode provided in the first tank; and a second electrode provided in the second tank. A wall surface of the nanopore has an ion adsorption preventing structure to prevent desorption/adsorption of an ion contained in a solution filling the first tank and/or the second tank, and a voltage is applied between the first and second electrodes to measure an ion current flowing through the nanopore.