PURPOSE: To increase a dredging efficiency, by installing an unloading conveyor and a changing load conveyor at the water's edge and transferring the dredged soil with a bucket chain type excavator by use of a plurality of barges and unloading the soil through the changing load conveyor.

CONSTITUTION: A bucket chain type excavator 10 and a loading conveyor 11 are arranged at the dredging point 1. And at the water's edge of an unloading point 2, a height-adjustable unloading conveyor 12 is installed and also a changing load conveyor 13 is installed on the sea corresponding to the conveyor 12. And further, a plurality of barges 14 are arranged to transfer the soil and sand dredged by the excavator 10 to the changing load conveyor 13 and further unload it. In this way, the dredging efficiency can be remarkably increased.