PURPOSE: To make it possible to wash stained sands and screen dregs selectively by a same apparatus in the washing treatment of a sewage treating field or the like by providing a barrier plate, a dust removing machine and a conduit for exhausting dusts along with a sewage out of a tank by an upward stream in a washing tank.

CONSTITUTION: Either a washing water and stained sands or screen dregs are selectively supplied into a washing tank 1 from a conveyor machine 7. By stirring blades 2 independently and respectively provided to an inner surface of both sides of the washing tank 1 and a washing water injected under a high pressure from a nozzle provided to an upper portion of the tank 1, screen dregs or the like are washed. The stained sands or the screen dregs washed in a stirring zone of the washing tank are separated into an org. and an inorg. substance and an org. substance is passed through a barrier plate in a condition floated in a sewage and reached to a separation zone. In said zone, an org. substance is exhausted from a dust removing machine 5 and an inorg. substance by a conveyor machine 6 respectively out of the tank as well as the sewage after washing is overflowed along with a floated org. substance from an upper end side of a conduit 8 to be exhausted and an org. substance is certainly removed.