To provide a large floating body having sufficient structural strength and reducible in oscillation even in a wide range of wave cycles and high wave by efficiently dissipating wave by a wave dissipating member of simple structure provided at the large floating body without installing a fixed breakwater or the like.

A wave upper side front end 1a of a large floating body 1 floating on the ocean is provided with a wave dissipating member 4 having a vertical plate 5 piercing the sea level and extending downward from the bottom face 1b of the large floating body 1, and a submerged horizontal plate 6 extending longitudinally from the lower end of the vertical plate 5. A stress concentration part, caused by moment of wave, of the wave dissipating member 4 is reinforced using support members 10a, 10b.