PURPOSE: To improve sporty enjoyment by closely mounting to both right and left ship sides in an upper part from the draft line of a ship body a folding airfoil able to be extended to the outside and restored.

CONSTITUTION: A folding airfoil is mounted in its main bones 2, 2' closely in the vicinity of an upper end of both sides 1, 1' of a ship body 1. This airfoil is extended by links 3, 3 to a position 2', 2' with a rotary axis X serving as the center, forming a wing surface shape by extending a thin film 5. Thus by controlling the link 3 easily extending and restoring the airfoil, a boat enables water sailing and floating in the air to be freely selected and sporty interest to be improved.