To provide a water stop instrument which can be easily stored when it is not used, which can be easily assembled in the field, and which can temporarily stop the water flowing into a passage or a clearance.

A plurality of rod-shaped aggregates 1 have the same shape, and have a horizontal part 1a and a rising part 1b. The rising part 1b is extended from one end of the horizontal part 1a and is raised at an acute angle so that it is returned to the horizontal part 1a side, A sheet member 3 covers the space between the horizontal parts 1a and the space between the rising parts 1b of the rod-shaped aggregates 1, and has a fixing part which fixes the rod-shaped aggregates 1 when the rod-shaped aggregates 1 are placed at intervals in a similar direction.