PURPOSE: To simultaneously perform a course control of a ship and its longitudinal and lateral attitude control while contriving the improvement of propulsive efficiency with less rudder resistance by providing not a rudder plate behind a stern propeller but every one separately controllable rudder in each longitudinal side of bottom part ship body.

CONSTITUTION: Separately controllable rudders 3a, 3b, passing through the center of gravity of a ship, are overhung in every longitudinal side of a bottom part ship body diagonally (about 45°) to the bottom, and these two sheets of rudders 3a, 3b are adjusted in their angle. While respectively paired every two sheets of rudders 3a', 3b' are overhung longitudinally in the bottom part ship body diagonally to the bottom, forming each rudder separately controllable. Thus, propulsive efficiency is improved. Simultaneously, even an attitude control in longitudinal and lateral directions can be attained.