PURPOSE: To raise the efficiency of dredging work by a method in which a wire for forward advancement is wound up by a winch for forward advancement, a dredger is advanced, a wire for swinging is wound up by a winch for swinging to left and right sides of the ship, and the dredger is swung to both sides.

CONSTITUTION: Wires 8 and 8' for forward advancement are wound up by winches 11 and 11' for forward advancement, and a dredger 7 is advanced. A wire 12 for swinging the left side board is wound up by a winch 13 for swinging the left side, and a wire 12' for swinging right side is sent out. Whereupon, the dredger 7 is swung from the right side to the left side between the wires 8 and 8'. During the period, a bucket 15 is driven to dredge the bottom under water. The dredger 7 is then advanced, the wire 12' for swinging the right side is wound up by the winch 13' for swinging the right side, and the wire 12 for swinging the left side is sent out. Whereupon, the dredger 7 is swung from the left side to the right side direction. During the above mentioned period, dredging work is performed by the bucket 14.