To effectively and uniformly perform frictional electrification of plastic pieces.

A frictional electrification device 11 electrifies plastic pieces fed to an electrostatic separator. A plastics charging opening 23 is formed in a top face of an vertically disposed cylindrical electrifying container 21 and a plastics discharging opening 27 capable of being freely opened and closed is formed in a bottom face. The electrifying container 21 is provided with stirring blades 29 rotated by a rotative driving device 31 through a stirring shaft 28. The inner face of the container 21 and the stirring blades 29 are coated with an anti-frictional resin, and a large number of outside air injection holes 34 are provided in the inner peripheral face of the container 21 for injecting air towards the axial center side. By opposing the air injected from the outside air injection holes against a centrifugal force applied to the plastics pieces by the stirring blades the plastics are prevented from forming lumps on an outer peripheral part.