To improve propulsion performance by attaching a fin which generates thrust in the forward motion direction by utilizing rising, falling, and swirling flows near a rudder surface.

This finned rudder 10 is disposed rearward of a screw propeller that rotates clockwise as viewed from a stern side during forward motion for changing the course of a ship 1 and provided with a first fin 12 and a second fin 14 in respective rudder surfaces 11, 13. One end of the first fin 12 is attached at a position higher than a center position of the screw propeller on a leading edge side of a central portion of the rudder surface 11, and one end of the second fin 14 is attached at a position lower than the center position of the screw propeller on the leading edge side of the central portion of the rudder surface 13. The other end of the first fin 12 extends at an upward inclination to a position inside the rotation radius of the screw propeller where the upward flow is strong, and the other end of the second fin 14 extends horizontally to a position inside the rotation radius of the screw propeller where the downward flow is strong.