To provide an elevation/floating structure excellent in wave surface following property by suppressing swing, particularly synchronous swing.

When a wavelength in the swinging of a buoy in synchronization with waves is Lwo, (a) the diameter Df of a float 1 is 50 to 70% of the wavelength Lwo, (b) the height Hf of the float 1 is 7 to 8% of the wavelength Lwo, and (c) a freeboard fa of the float 1 is 4 to 6% of the Lwo. If all of the conditions (a) to (c) are satisfied, the best wave surface following property is provided, and the most ideal buoy can be provided.