A propulsion device for a ship is introduced. The propulsion device for the ship comprises a duct having a nose corresponding to the front vertex of a hydrofoil cross-section and a tail corresponding to the rear vertex of the hydrofoil cross-section, wherein the shape of the duct cross-section comprises: an outer surface formed upward in a convex shape at the front end of the duct and formed downward in a concave shape at the rear end of the duct; an inner front part of the duct formed downward in a convex shape at the front end of the duct; an inner rear part of the duct formed downward in a convex shape at the rear end of the duct; and a parallel part for connecting the inner forward part and the inner backward part in parallel to each other.