To increase a construction efficiency.

In this cofferdam closure method, the outer periphery of a bridge pier 1 is surrounded by a cylindrical cofferdam closure wall 14, the inside water is drained, and a reinforcing work is done. After completion of the works, the cofferdam closure wall 14 is removed. The wall is formed of a plurality of vertically divided panel units 16. When forming the cofferdam wall, a guide frame 10 is put on a footing 2 of a bridge 1 and the inside face of the respective panel units 16 is engaged with the guide frame 10 to vertically support the panel units 16. Next, the lower end side of the panel unit 16 is fixed into the water bottom ground 3 along the outer periphery of the footing 2 by placing concrete so as to cutoff. In this time, cutoff packings are interposed between the peripherally adjacent panel units 16 to secure waterproofness and the panel units 16 are connected in the peripheral direction to form a cylindrical shape.