PURPOSE: To house a driving-shaft strand and a pulsation device in a shaft-like casing without installing an additional space on a steering propeller-driving device in a hull by moving the driving shaft strand and a pulsation device attached to it past the side of a motor.

CONSTITUTION: A driving-shaft strand 3 can be adjusted in the upward direction past a motor 2 in its position. A steering propeller 1 is completely placed on the bottom 13 of a hull, and the motor 2 and the upper region of the driving- shaft strand 3 are placed in a row in a shaft-like casing 12, though the driving- shaft strand is not projected up beyond the shaft-like casing 12. Compared with prior arts, all variable propeller devices or a steering propeller-driving device and the shaft-like casing 12 can be built lower by the height H of the motor, and no additional space must be free above the steering propeller-driving shaft in the body of the hull.