An object of the present invention is to provide a water-blocking device that can be easily installed in a short time and can surely prevent water intrusion. The water-blocking device 1 includes a water-blocking plate 2, a first band 3 for fixing the water-blocking plate 2 to the installation surface 10, at least one first band passer 5 mounted near an installation location of the water-blocking plate on the installation surface 10, third band passers 7 mounted on left and right walls, etc., 11, 12 defining an entrance or exit S, and second bands 4 for fixing the water-blocking plate 2 to the walls, etc., 11, 12. The water-blocking plate 2 is provided with at least one second band passer 6 and fourth band passers 8. The first band 3 is wound through the first band passer 5 and the second band passer 6 in such a manner that a pressing force toward the installation surface 10 is exerted onto the water-blocking plate 2. The second bands 4 are wound through third band passers 7 and fourth band passers 8 in such a manner that pressing forces toward the walls, etc., 11, 12, are exerted onto the water-blocking plate 2.