To select plastic pieces by kind accurately at a lower voltage as compared with a conventional method.

Plastic pieces are supplied into a charging container 3 and contacted frictionally with an inside cylinder 3a of standard plastic at an intermediate position in an electrification rank by a revolving contact air A, and the plastic pieces superior to standard plastic in the electrification rank are charged positively, while the plastic pieces inferior in the electrification rank are charged negatively. Next the plastic pieces are passed through an electrostatic field R for separation which is formed by a drum electrode 11 and a counter electrode 13 to be separated by being attracted or repulsed by the electrodes 11, 13, utilizing the attractive force by the polarity and voltage of the plastic pieces.