PURPOSE: To provide an apparatus for electrostatic classification which can treat a large amount of aerosol and has an excellent mono-dispersibility for an optional particle size and an improved space efficiency by forming a unit main body of a flat rectangular tube.

CONSTITUTION: Each of electrostatic classification units 10 comprises a unit main body 11 of a flat rectangular tube forming a downstream passage for charged aerosol particles in it, an electrode 14 of a plane plate generating an electric field perpendicular to the flat surface of the unit main body 11 in the downstream passage, an aerosol supply part 13 forming an aerosol supply slit 13A, and an aerosol collecting part 15 forming an aerosol collecting slit 15A in parallel with the aerosol supply slit 13A. The electrostatic classification units 10 are arranged so that the flat planes of the units confront each other. The aerosol particles having a constant particle size and electric charge are moved in the direction perpendicular to the flat plane of the unit main body 11, forming a narrow flow. The particles are lastly corrected into the aerosol collecting slit 15A.