To provide sure water cut-off performance, regardless of the existence of unevenness and an inclination of an existing footing, when cutting off water by placing a temporary closing work on the existing footing of an underwater structure.

This temporary closing work comprises a temporary closing wall body 18 formed in annular shape out of a plurality of panels 20 manufactured in advance, a stand 22 integrally arranged in an annular shape inside a lower part of the temporary closing wall body, and a water cut-off means 28 arranged in a bottom part water cut-off position of the temporary closing wall body and cutting off the water between the means and the underwater structure 10. The temporary closing wall body surrounds the underwater structure, and the stand is placed on the outer peripheral edge of the existing footing 14. A bag body 30 for placing underwater concrete inside is arranged in an annular shape in the bottom part water cut-off position of the temporary closing wall body as the water cut-off means. By placing the underwater concrete inside the bag body after being immersed by placing the stand on the outer peripheral edge of the existing footing of the under water structure, the water is cut off on the lower end side of the temporary closing work by expansively forming the water cut-off means between the underwater structure and the temporary closing wall body.