To provide a waterproofing tool capable of being easily installed by only supplying water, quickly coping with waterproofing for a long distance, facilitating the manufacture, being applied to mass production and being stored by folding it.

The waterproofing tool is formed of a foldable cylindrical waterproofed bag body, and has both ends of the cylindrical waterproofed bag body which are closed and water supply/drain ports. The tools are jointed with one another for use. A joint section is covered with a sheet with a surface fastener. The cylindrical waterproofed bag body is formed of a rubber material using a woven cloth as a reinforcing layer. A material showing a columnar shape in use is preferred.