PURPOSE: To classify a gas in which only those particles whose specific mass is in a specified range float up by continuously sucking gas between cylindrical outside and inside electrodes that rotate about a common axis of symmetry, and utilizing the balance between an electrostatic force and a centrifugal force that work on the particles in the gas.

CONSTITUTION: An outside frame 1 is secured to a rotor 2 and rotated by a motor. A cylindrical outside electrode 3 is provided on the frame 1 and an inside frame 8 is incorporated into the frame 1, and an inside electrode 9 is provided on the side of the frame 8. Voltages V from a DC power source 17 are applied to the electrodes 3, 9 via brushes 18, 19 to create an electrostatic field within an operating space 15. An insulator 16 is held in place inside the operating space 15, and an aerosol to be introduced is rotated at the same speed as the frames 1, 8. The aerosol is continuously introduced into the space 15 from an inlet pipe 7, and then discharged through an exhaust pipe 14, so that a gas, in which only those particles whose specific mass m/q (mass/ charge) is in a specified range float up, can be continuously classified by virtue of the balance between an electrostatic force and a centrifugal force that work on the particles in the aerosol.