Rankine cycle system

A Rankine cycle system (101) mounted on a vehicle includes a Rankine cycle circuit (100), a pressure detector (121), a temperature detector (122) and a controller (119). The Rankine cycle circuit includes a fluid expansion device (114), a fluid transferring device (111), first (1) and second (2) passages, a heater (112,113), a cooling device (115), a bypass passage (3) and a flow regulating valve (120). The bypass passage connects the first passage and the second passage, and in which the flow regulating valve is provided for opening and closing the bypass passage. The controller is connected to the flow regulating valve for controlling an operation of the flow regulating valve and to the pressure and temperature detectors and for receiving signals of pressure and temperature from the pressure and temperature detectors, respectively. The controller controls the operation of the flow regulating valve based on a superheat degree of the working fluid calculated from the signals of the pressure and temperature.