PURPOSE: To fix a sheet only by injecting water by mounting a tubular water storage section along a sheet edge and installing a suction and drain valve communicated with the water storage section.

CONSTITUTION: One cloth made of a synthetic resin is cut in a rectangular shape, the edges of four sides are bent towards the inside respectively and an end section is welded through heat sealing working, and a tubular water storage section 2 is formed extending over the whole circumference of a protective sheet 1. A cock 3 for supplying and draining water is set up at a proper place at the end section of the water storage section 2 while being communicated with the inside of the water storage section 2. An object is covered with the protective sheet 1 first, city water is injected from the cock 3 for supplying and draining water and the water storage section 2 is filled with water. Accordingly, the whole circumference of the edge of the protective sheet 1 is fixed under the state, in which the whole circumference of the edge of the sheet 1 is weighted, thus obtaining sufficient sealing properties. When water is drained and the sheet 1 is folded at the time of nonuse, maintenance is facilitated.