PURPOSE: To assure an engine adapted to be higher in efficiency of utilizing steam by arranging a pair of pistons while disposing a central high pressure chamber therebetween and driving the pistons with use of a high pressure chamber, while rotating an engine body by making use of low pressure steam from the high pressure chamber.

CONSTITUTION: A pair of pistons 10 are housed in a cylindrical engine body 1 in a confronting relation while holding a central high pressure chamber 2 therebetween. An introduction hole 3 for high pressure steam is formed in a center of the high pressure chamber 2, while an exhaust hole 4 is formed in said chamber at both sides of the introduction hole 3. An outlet of the exhaust hole 4 is bent in a direction of a tangential line of the chamber to provide a nozzle 5, and a bucket 13 is formed integrally with the engine body 1 on an outer periphery of the body spaced leaving an interval for interposing a stationary blade (not shown) on the engine body. The pistons are reciprocated and rotated by profitably employing pressure of high pressure steam supplied from the introduction holes 3 into the high pressure chamber 2, and rotating force yielded as such as well as rotating force of the bucket 13 produced due to waste gas pressure injected from said nozzle 5 are utilized for power to drive an engine.