A mechanism to accelerate hot water in a pipe by boiling of liquid freon injected in the hot water was developed with the final object being to drive a Pelton wheel. Characteristics of the acceleration were measured by using a convergent nozzle, a convergent-parallel nozzle and two convergent-divergent nozzles with different divergent angles, and the relation between the reaction force of the jet and the flow rate of the liquid freon was obtained. When using the convergent nozzle, the experimental values were lower than the theoretical ones. In the case of other nozzles, the experimental values were higher than the theoretical ones under certain conditions such as high temperature and liquid freon injection of small amounts- It is considered that this phenomenon comes from the addition of acceleration of water vapor which is generated at the nozzle throat because water is agitated strongly by the freon gas. The convergent-divergent nozzle with a small divergent angle shows excellent characteristics.