To provide a construction method by which a diving operation for water cut-off is reduced, water can be surely stopped, and cofferdam can be easily withdrawn.

When a cofferdam frame 2 is sunkenly provided in the water, a water barrier material 4 made of sponge is interposed between the lower end edge 2a and the bottom of the water 1. A refrigerating piping 5 is turningly provided in the water cut-off material 4, both the ends are connected to a refrigerator 6 provided on the ground or on the water, and hence the refrigerating piping functions as an evaporator in a refrigerating cycle. Hereby, when the refrigerator 6 is operated, the interior of the water cut-off material 4 and earth and sand, sludge, and the like on the bottom of the water contacted with the water cut-off material 4 are frozen by the heat absorbing effect of refrigerant supplied to the refrigerating piping 5, and water is perfectly stopped between the cofferdam frame 2 and the bottom of the water 1. Hereby, by draining water in the inside space of the cofferdam frame 2 to the outside water area W, a space S for building work is formed.