To reduce the oscillation of a hull under stoppage by generating a lift on a hydrofoil.

A hydrofoil of a ship is formed with an upper and lower hydrofoils 3 and 4 installed on the underside of struts 1 and 2 attached under a hull, respectively, ailerons 3a, 3b, 4a, and 4b are installed on the upper and lower hydrofoils 3 and 4, respectively, and the ailerons are arranged differently between front and rear sides for each of the upper and lower hydrofoils 3 and 4. Also either of the upper and lower hydrofoils 3 and 4 is installed on the strut rotatably about a horizontal axis. With this structure, a lift to suppress a vertical oscillating moment can be generated on either or both of the upper and lower hydrofoils even when the hull is under stoppage.