PURPOSE: To easily screen wood chips by throwing matters to be screened from an upper part of one side of a wind tunnel to other side, screening and classifying them by screening wind, which crosses the throwing direction rectangularly from an upper part of a throwing route.

CONSTITUTION: Wood chips from which sands or metals are removed by a pre-screening machine are put into a supplying device 35 of a throwing wind selecting device 25. The stacked wood chips are delivered in sequence by a fixed quantity at a timber by delivery rolls 51, 52, 53 and supplied to a starting end of a throwing device 32 by a carry-out belt 47. The chips are thrown from a terminal end of a conveyor belt 45 to other end of a wind tunnel 29, classified by the distances according to their specific gravities, and allowed to fall. At this time, throwing routes are classified according to the specific gravities by a screening wind which goes to a slanting lower part to be formed in between a blowing port 33 and an inlet port 34. Accordingly, in the process of screening according to the specific gravities by throwing, the wood chips are blown back by the screening wind which goes in a direction reverse to the throwing direction and crosses toward this side of the slanting lower part, so that light matters such as papers are assuredly separated from the chips and waste chips of high quality can be recovered.