A particle count measurement device for measuring a particle count concentration of an aerosol flowing through a measurement region, the particle count measurement device comprising: a unipolar charging section inside the measurement region; an ion trap arranged inside the measurement region, downstream of the unipolar charging section, the ion trap including an ion trap electrode for generating an electric field that draws only gas ions in the aerosol; an exhaust mechanism outside the measurement region, the exhaust mechanism being configured to discharge the aerosol from the measurement region at a constant flow rate; and an ammeter for detecting, as a measurement value corresponding to the particle count concentration, a difference between current supplied by the unipolar charging section and current flowing into the ion trap, the particle count measurement device being characterised in that it comprises a preprocessing section configured to place the aerosol introduced into the measurement region in an electrical state of any of a neutralized state, a positively charged state or a negatively charged state, wherein the unipolar charging section is configured to place the aerosol in an electrical state different from the electrical state at a time of introduction into the measurement region, the particle count measurement device further being characterised in that it comprises a pair of counter electrodes (52a, 52b) arranged between the ion trap and an outlet of the measurement region, the pair of counter electrodes (52a, 52b) being arranged in parallel with a flow of the aerosol; and a classification power supply for generating, at the counter electrodes, an electric field for drawing charged particles having particle diameters smaller than a predetermined particle diameter, wherein the ammeter is configured to measure a difference between current supplied by the unipolar charging section and current flowing into the ion trap and the counter electrodes to measure a particle count concentration of particles having particle diameters equal to or greater than the predetermined particle diameter. a unipolar charging section inside the measurement region; an ion trap arranged inside the measurement region, downstream of the unipolar charging section, the ion trap including an ion trap electrode for generating an electric field that draws only gas ions in the aerosol; an exhaust mechanism outside the measurement region, the exhaust mechanism being configured to discharge the aerosol from the measurement region at a constant flow rate; and an ammeter for detecting, as a measurement value corresponding to the particle count concentration, a difference between current supplied by the unipolar charging section and current flowing into the ion trap, the particle count measurement device being characterised in that it comprises a preprocessing section configured to place the aerosol introduced into the measurement region in an electrical state of any of a neutralized state, a positively charged state or a negatively charged state, wherein the unipolar charging section is configured to place the aerosol in an electrical state different from the electrical state at a time of introduction into the measurement region, the particle count measurement device further being characterised in that it comprises a pair of counter electrodes (52a, 52b) arranged between the ion trap and an outlet of the measurement region, the pair of counter electrodes (52a, 52b) being arranged in parallel with a flow of the aerosol; and a classification power supply for generating, at the counter electrodes, an electric field for drawing charged particles having particle diameters smaller than a predetermined particle diameter, wherein the ammeter is configured to measure a difference between current supplied by the unipolar charging section and current flowing into the ion trap and the counter electrodes to measure a particle count concentration of particles having particle diameters equal to or greater than the predetermined particle diameter.