PURPOSE: To make it possible to perform accurate steering of a ship and steering of good steering efficiency by providing two kinds of propelling devices in combination.

CONSTITUTION: In the case of precise steering, a sluice valve 7 is closed, a clutch 10 is released and a clutch 13 is applied. By this procedure, a generator 15 is driven mechanically by means of a transmission device 14 having the clutch 13 from a propelling engine 9. A motor 21 driven through a circuit 22 by the generator 15. By the rotation of the motor 21, an auxiliary propeller 19 is mechanically rotated by the rotation of the motor 21 through the transmission device 20. In the case where the vessel nevigates on the sea, the sluice valve 7 is opened, and the clutch 10 is applied and the clutch 13 is released. Upon this occasion, a main propeller 12 in a water stream pipe 2 is mechanically driven through a transmission device 11. Therefore, nevigation of high propelling efficiency is achieved.