PURPOSE: To eliminate the need to discharge the stored water of a dam when dredged sand is discharged from the dam to reduce the influence on downstream areas of the dam or on the production of electric power and water works, eliminate the provision of sand discharge gates or water sealing gates, water- tightness of which is difficult to maintain, make power source devices smaller, and smoothly transfer the dredged sand even over a steep slope.

CONSTITUTION: An endless wire 12 is driven to circulate each sand transfer truck 3 between a loading yard (a) above a dam 6 and a sand discharge pool (b) below the dam so that sand containing water 1 (sand + water having specific gravity of 1.0-2.0) dredged from the dam is loaded onto a truck 3 having reached the yard (a). The sands 1 carried by the truck 3 having got into the pool is discharged therefrom to load only the discharged water (specific gravity is 1.0-1.1), from which the sand has been separated, into the truck. As a result, in the drive system of trucks 3, the weight of the trucks going down from the yard (a) to the pool (b) is transmitted to the trucks 3 of the whole circulation system through the wire 12, so that the trucks 3 are circulated along a forward and backward track 12.