Provided are an apparatus and a system for classifying particles. The apparatus for classifying particles includes: an internal electrode which has a column shape; an external electrode which is spaced apart from the internal electrode and disposed to surround the internal electrode, and generates an electric field through an interaction with the internal electrode; and an aerosol supply unit which supplies aerosol particles to a separation space between the internal electrode and the external electrode, in which the separation space, through which the aerosol particles are introduced into the particle classifying apparatus and flow, is formed to be narrowed toward a lower aerosol flow side from an upper aerosol flow side into which the aerosol particles are introduced.