To prevent a water path from being generated in a cut-off agent layer, if a large quantity of water flows in by arranging a water permeable sheet on both surfaces of the cut-off agent layer laminated in such a manner that a water-absorbing material whose water-absorptive rate is the highest among two or more different water-absorbing materials whose water-absorbing rates are different, is located on at least, one of the surfaces of the cut-off agent layer.

An adhesive is applied to a needle punching unwoven fabric 1A as a water-permeable sheet, then sodium polyacrylate 2A with high water- absorbing rate is sprayed over the adhesive coat, and a reinforcing sheet 3A is laid over this sodium polyacrylate 2A. In addition, bentonite 5 with a low water-absorbing rate is sprayed over the reinforcing sheet 3A and the bentonite layer 5 is lightly pressed with a roll 16. Further, a composite sheet 3B is the needle punching unwoven fabric 1B and the sodium polyacrylate 2B is laminated on the bentonite layer 5 in such a manner that the sodium polyacrylate 2B is set to face the bentonite layer 5. Finally, this laminate is subjected to a needle punching process and the adhesive is cured to obtain the cut-off agent 6.