In an engine, a rotor having a folded jet pipe is rotatably supported in a sealed container filled with a liquid. A heating portion is inserted in a center cylinder at the center of the rotor, and a fluid of a high temperature is passed therethrough to vaporize the liquid sucked through the suction pipe of the rotor. A mixture of steam and liquid is jetted from the jet pipe due to the pressure of the steam that is vaporized to rotate the rotor. A check valve for jetting and a check valve for suction are disposed at the ends of the jet pipe and the suction pipe. The jetted steam is guided to a condenser disposed on the sealed container, and is condensed and is refluxed into the sealed container. A vacuum pump is connected to the condenser, and the pressure in the sealed container is held at the saturated steam pressure.