PURPOSE: To improve the efficiency of sheet laying operation by attaching a rope or a net, to which plate-shaped floats are inserted and held, onto the surface of a sheet laid on a filled-up land etc., spreading the sheet, and detaching the floats.

CONSTITUTION: Ropes 4, to which plate-shaped floats 5 are inserted and held, are attached on the whole or a part of the surface of a water-barrier sheet 1 laid extending over the internal surface of a revetment and the bottom of water. Nets can also be mounted in place of the ropes 4. The plate-shaped floats 5 consisting of urethane foams and air bags are inserted among the sheet 1 and the ropes 4, the sheet 1 is spread while being floated on the surface of water, the floats 5 are detached, and the sheet 1 is sunk. Parts of the floats 5 are used as weight bags and the floats 5 are sunk as they are left as they are fixed on the sheet 1 at that time, thus also preventing the floating of the sheet 1. Accordingly, the water-barrier sheet 1 can be laid efficiently.