PURPOSE: To increase the recovery ratio of purified compost as wel as to reduce the mixing of impurities by classifying a mixture to be sorted according to a particle size prior to supplying the mixture to be sorted to a sorting stage.

CONSTITUTION: On the upper part of the housing 1 of an electrostatic sorting apparatus, a hopper 51 storing a mixture M to be sorted conveyed by a stock material supply conveyor 81 is placed and, prior to supplying the same to a sorting stage 11 through a charging feeder 52 and a supply feeder 53, the mixture M to be sorted is sorted according to a particle size and scraped off onto the stage 11 by a scraper 41. As described above, because compost and impurities are preliminarily classified according to a particle size and electrostatic sorting is carried out thereafter, the recovery ratio of purified compost is increased as well as the mixing ratio of impurities into the purified compost is reduced.