Abstract: A steering device in which a rudder plate is vertically suspended at a positive minimum distance ? from an outer edge of a propeller having a radius R from a steering shaft which is biaxially arranged and symmetrically rotates around a screw shaft within a propeller radius R from a screw shaft center, on a propeller rotation plane, and can be turned from aside of a propeller to a downstream of the propeller by rotation of the steering shafts, each of which is driven independently by two hydraulic driving mechanisms, and the steering device is characterized in that the steering action is divided into two modes: the two-independent mode and the two-same direction modes, and each mode is adapted as follows: at the time of ahead condition, each one of the two rudder plates is retained on both sides of a propeller parallel with a ship axis, and at the time of veering of the two-same direction mode, a rudder plate opposite to a veering direction turns 45° from aside of the propeller to the downstream of the propell