A steering device allows a ship to travel efficiently. A port side rudder plate has a left front rudder plate fixed to a lower portion of a stern and a left rear rudder plate. A starboard side rudder plate has a right front rudder plate fixed to the lower portion of the stern and a right rear rudder plate. The left rear rudder plate is supported by a rear portion of the left front rudder plate and a left steering shaft fixed to the left rear rudder plate. The right rear rudder plate is supported by a rear portion of the right front rudder plate. A right steering shaft fixed to the right rear rudder plate. In a rear view, lower end portions of the port side rudder plate and the starboard side rudder plate are at a lower end portion of an outer peripheral portion of the propeller.