A steering device comprising: a port side rudder plate arranged on a port side of a propeller of a ship; and a starboard side rudder plate arranged on a starboard side of the propeller, wherein the port side rudder plate is formed of a left front rudder plate fixed to a lower portion of a stern and extending in a vertical direction and a left rear rudder plate provided behind the left front rudder plate and extending in the vertical direction, the starboard side rudder plate is formed of a right front rudder plate fixed to the lower portion of the stern and extending in the vertical direction and a right rear rudder plate provided behind the right front rudder plate and extending in the vertical direction, the left rear rudder plate is turnably supported by a rear portion of the left front rudder plate and a left steering shaft fixed to the left rear rudder plate and extending in the vertical direction, the right rear rudder plate is turnably supported by a rear portion of the right front rudder plate and a right steering shaft fixed to the right rear rudder plate and extending in the vertical direction, characterized in that the left rear rudder plate is formed of a left vertical portion provided behind the left front rudder plate and a left inclined portion extending downward right from a lower portion of the left vertical portion, the right rear rudder plate is formed of a right vertical portion provided behind the right front rudder plate and a right inclined portion extending downward left from a lower portion of the right vertical portion, in a side view, the left inclined portion extends from a front portion of the left front rudder plate to a rear portion of the left vertical portion and the right inclined portion extends from a front portion of the right front rudder plate to a rear portion of the right vertical portion, and in the rear view, lower end portions of the left inclined portion and the right inclined portion are located at a lower end portion of the rotation outer peripheral portion of the propeller. a port side rudder plate arranged on a port side of a propeller of a ship; and a starboard side rudder plate arranged on a starboard side of the propeller, wherein the port side rudder plate is formed of a left front rudder plate fixed to a lower portion of a stern and extending in a vertical direction and a left rear rudder plate provided behind the left front rudder plate and extending in the vertical direction, the starboard side rudder plate is formed of a right front rudder plate fixed to the lower portion of the stern and extending in the vertical direction and a right rear rudder plate provided behind the right front rudder plate and extending in the vertical direction, the left rear rudder plate is turnably supported by a rear portion of the left front rudder plate and a left steering shaft fixed to the left rear rudder plate and extending in the vertical direction, the right rear rudder plate is turnably supported by a rear portion of the right front rudder plate and a right steering shaft fixed to the right rear rudder plate and extending in the vertical direction, characterized in that the left rear rudder plate is formed of a left vertical portion provided behind the left front rudder plate and a left inclined portion extending downward right from a lower portion of the left vertical portion, the right rear rudder plate is formed of a right vertical portion provided behind the right front rudder plate and a right inclined portion extending downward left from a lower portion of the right vertical portion, in a side view, the left inclined portion extends from a front portion of the left front rudder plate to a rear portion of the left vertical portion and the right inclined portion extends from a front portion of the right front rudder plate to a rear portion of the right vertical portion, and in the rear view, lower end portions of the left inclined portion and the right inclined portion are located at a lower end portion of the rotation outer peripheral portion of the propeller.