To sufficiently resist earth pressure without particularly increasing the sections of coffering materials even when a ground surface on the front side is deepened and earth pressure from filled sand charged among the coffering materials by steel sheet piles or the like is augmented when a part under a water surface is to be coffered by a double wall cofferdam construction method, to facilitate handling, reduce the manufacturing cost of the coffering materials, and to improve workability.

The cofferdam device is used for the double wall cofferdam construction method, in which coffering materials such as steel sheet piles 11 or the like driven in two rows at intervals are connected mutually by tie materials. Binding sections 3a-3c for PC steel wires 1a, 1b as the tie materials are installed to the coffering materials 11 at a plurality of places along the height direction of the coffering materials, and connected to fixing sections, where a plurality of these binding sections are interlocked mutually and bound.