Abstract: The inventive wave dissipating device includes a sea surface sheet to be installed along a sea surface, a sea submergence sheet to be installed below the sea surface sheet generally parallel to the sea surface sheet in sea, and connection ropes connecting the sheets to each other. The sea surface sheet has a predetermined area, and functions as a float to float on the sea surface in an installed state. The sea submergence sheet has the same area as the sea surface sheet When the sea surface sheet is likely to be moved by the tsunami, the sea submergence sheet functions as a weight to prevent the movement of the sea surface sheet, thereby dissipating the wave.