To provide a Rankine cycle device capable of immediately lowering a pressure to maintain every device and resume the operation when a high pressure exceeding an allowable limit pressure of an expander or an evaporator is produced within a circuit, as well as capable of lowering a temperature and a pressure of working medium itself when the high-temperature/high-pressure working medium should be discharged to the outside of the circuit for lowering the pressure so as to reduce influence of the discharged working medium on peripheral equipments such as a discharger.

The Rankine cycle device 10 is provided with a discharging valve device 203 in a closed circuit where the working medium is in a liquid phase, between a supplying pump 44 and the evaporator 11 for discharging the working medium to the outside of the closed circuit when an inner pressure in the closed circuit is at least higher than a set pressure set to be lower than the allowable limit pressure of the expander 12 or the evaporator 11.