To further improve performance for assisting the propulsive force of a ship in a ship with a propeller provided on a stern part.

The ship includes the propeller 3 provided on the stern part 2, a circular duct 5 which is arranged above central positions X of stern vertical vortexes S generated on the front side of the propeller 3 and on the stern part 2 and which has a diameter increasing toward the front side from the rear side of the ship, and main fins 6 extending between both lower ends of the duct 5 and a side surface of the stern part 2 in the radial direction of the propeller 3 and inclining upwardly toward the front side from the rear side of the ship.