To solve the following problem: in generating electric power with heat source fluid at a low temperature, a difference between heat source fluid and cooling fluid temperatures at the front and rear of a heat exchanger is set to be low because a difference of temperatures at the front and rear of a turbine is not larger than that between an outlet temperature of heat source fluid and an inlet temperature of cooling fluid; therefore, a large amount of heat source fluid and cooling fluid are required and the temperature lowering quantity of the heat source fluid is small and an outlet temperature is difficult to control, for example, in the case that a temperature of hot spring is high, its temperature from the power generation unit is high even after power generation is performed with the hot spring; therefore, cooling is required.

By flowing heat source fluid into a combined unit of a plurality of evaporators and a power generation turbine in a series manner, a difference between temperatures the front and rear of a power generation unit increases in a magnification ratio of the number of power generation units.