To reduce suction resistance and to decrease an installation area.

A propulsion unit is such that after water is sucked from the suction casing 3 of a ship bottom and a swirl flow pressurized by the impeller 6 of a pump casing 5 is straightened by a guide vane 7, pressure water is jetted to the rear of a stern from a discharge casing 8 to propel a boat. In the propulsion unit, the output shaft of an engine 12 for drive placed above a pump casing and a suspending shaft are coupled together trough a vertical shaft conversion drive device 13 and a drive shaft 21 coupled to the impeller is extended to the rear of the impeller and pivotally supported at the bearing case 22 of the guide vane. Further, since the drive shaft of the impeller and the suspending support shaft are coupled together through a horizontal shaft conversion derive device 23, the axis of the impeller disposed at the pump casing is lowered, and by lengthening the length of the suction casing, an inflow passage is formed in a gentle state.