PURPOSE: To obtain non-polluting energy by a method wherein the descending motion of buckets carrying dumping matters is converted into the electric power through a proper generation device.

CONSTITUTION: At first, rocks 2 and the like dumped through a vertical shaft 3 are carried to a transfer device 20 arranged offshore by means of the trucks of a transport device 4. Then the rocks are once ascend and then thrown in a conveyor (not shown) of a dumping device 21 from the trucks and through a chute (not shown) and the buckets of the transfer device 20. After that, the rocks are discharged into hoppers 29a, 29b, arranged along the side of the conveyor of the dumping device successively. When the bucket 31 of a throw-in part 30 is thrown in with the rocks to weigh the fixed weight, the bucket 31 descends, resulting in driving an oil-hydraulic pump 39, attached through a shaft with a drum (not shown), which is rotated with the descending motion of the bucket, to discharge pressure oil. The pressure oil is sent, through a pressure oil pipe 40, to an oil pressure controller 41 to drive an oil-hydraulic motor 42 in order to generate the electric power with a generator 43.