PURPOSE: To treat screenings without causing any trouble by incresing water flow rate by making use of a circulating circuit and using a washing vessel as a water flow trough, when the screenings out of the capacity are supplied at the rainfall or other time.

CONSTITUTION: In case when ordinary operation is performed, screenings are supplied by a feeder 2 to a washing vessel 1 according to its treating capacity, and while washing water is being supplied 3, high-pressure water is spouted from nozzles 5, thence they are scraped up by a dust remover 4 and discharged to outside of the vessel; at the same time, the soiled washing water is overflowed to outside the vessel. When the amount of the screenings supplied at the rainfall or other time reaches out of the capacity of the washing vessel, the nozzles 5 are stopped and a circulating pump 6 is operated to increase the water flow rate through a circulating pipe 7, so that the washing vessel 1 is used as a water flow trough and the outflow amount of screenings per unit time is thereby caused to increase.