In a steam engine having multiple main containers, first and second communication pipes are arranged in parallel to each other for respectively communication an auxiliary container with the main containers. Restricted portions and a first switching device are formed in the first communication pipe. The first communication pipe is closed during a start-up step of a starting operation of the engine, in order to prevent that an excess amount of working fluid may flow back from the auxiliary container to the main containers. As a result, a start-up time can be reduced.