PURPOSE: To start rapidly by a labor saving and power saving method, by providing a suction pipe in which the lower end opening is connected to the upper end and the rear end of an impeller member, a switch valve is inserted at the intermediate part, and the upper end opening is connected to a vacuum tank.

CONSTITUTION: While a shutter type valve 13 is installed to a discharge port 4 at the rear end of a duct 11, a vacuum tank 9 and the like to give a negative pressure to an impeller chamber 12 are provided. Prior to the starting, the pressure of the vacuum tank 9 is reduced by a vacuum pump 10. In this case, a switch valve 8 inserted to a suction pipe 14 is closed. And the shutter valve 13 is closed and the discharge port 4 is fully closed. By opening the switch valve 8, the sea water is sucked to the impeller chamber 12 from the water intake by the negative pressure of the vacuum tank 9 so as to fill the impeller chamber 12 with the sea water, and then an impeller 5 is rotated to start a water jet. When a water jet propelling device is started, the switch valve 8 is closed, while the shutter type valve 13 is fully opened.