To feed plastic pieces to an electrostatic separator via a triboelectrifying device without being accompanied with dust while using a dry cleaning device of a low cost.

The electrostatic separator of plastic is provided with the dry cleaning device the triboelectrifying device and an electrostatically separating equipment for classifying the plastic pieces and further a dust removing device 2 is provided between the dry cleaning device and the triboelectrifying device. The dust removing device 2 is provided with a mesh plate 36 for supporting the plastic piece from below, a mesh plate vibrating device 37 for vibrating the mesh plate 36, a dust sucking device 38 for sucking and removing the dust accompanying the plastic pieces via the mesh plate and a static eliminator 39.