A steam engine in which a liquid and a steam are jetted so that a rotor is turned by the reaction thereof, and the rotor having a well-balanced simple structure. In the steam engine, the rotor 5 having a plurality of bent flow paths 53A to 53D arranged at regular intervals therein is rotatably supported in a closed container 1 filled with the liquid being fitted onto a boss portion 11 of the closed container 1. The boss portion 11 is alternately forming slide-contact portions 11A having a steam feed port and recessed portions 11B. The steam fed into the bent flow path 53 from the steam feed port causes the liquid in the flow path to be jetted outward to rotate the rotor 5. The rotor 5 is of a point-symmetrical shape in cross section free of unbalanced weight, has no moving part, and is simple in structure. When the bent flow path 53 communicates with the recessed portion 11B, the steam remaining in the flow path is cooled and disappears, and the flow path is filled with the liquid.