PURPOSE: To provide a high-thrust propulsion device not depending much on the limited gas pressure (gas turbine) and the mechanical rotation (pump impeller) unavoidable with cavitation for the jet acceleration of the water jet propulsion device.

CONSTITUTION: A liquid (water) is fed from an opened intake port 3, it is pressurized by a pump impeller 8 in a duct 5 and spouted from a nozzle section 19, the condensing gas (steam) is condensed in contact with the liquid (water), and a condensation chamber 12 accelerating the water via the motion quantity of steam, a negative-pressure forming chamber 18 accelerating the water via the motion quantity of air when the gas (air) is brought into contact with the liquid (water) to make the surrounding negative pressure, and a jet port discharging a fluid are provided in the nozzle section 19.