A classification apparatus for classifying and separating particles having particle sizes within a predetermined range is disclosed. In a preferred embodiment of the classification apparatus, a center electrode (3) and an outside electrode (4) generate an electric field for classifying charged fine particles according to electric mobility. In the upper part of a housing (1), a sheath gas supply portion (7) is provided. An aerosol supply portion (11) has an introduction port (11a) provided on the outside electrode (4) side in a classification region (5), and supplies a charged aerosol at a constant flow rate through the introduction port (11a). On the downstream side in the flow of a sheath gas in the classification region (5), a larger-size particle discharge portion (13) is provided. The larger-size particle discharge portion (13) has a discharge port (13a) provided on the outside electrode (4) side, and discharges charged fine particles, which are contained in the classified charged aerosol and have particle sizes larger than a predetermined particle size, together with part of the sheath gas at a constant flow rate. A detector (18) is provided downstream of the housing (1) to detect the number of remaining charged fine particles contained in the sheath gas introduced thereinto as the quantity of electricity.