Rankine cycle system, the expansion system, and the expander

To increase the reliability of the Rankine cycle system using a closed type expander, a Rankine cycle system of the present disclosure (100a) includes a pump (1), the heater (2), an expander (3), heat radiator (5), and a cooling passage (8). Expander (3), an expansion mechanism that takes power from the working fluid (11), a generator (12), an expansion mechanism (11) and a sealed container that houses the generator (12) (10), a first supply port and (34a), a first outlet and (35a), a second supply port and (30a), a second outlet and (31a), a. Radiator (5) is connected to a pump (1) by passage to cool the discharged working fluid from the second outlet (31a). Cooling path (8) has a first discharge port a cooler for cooling the exhaust working fluid from (35a) (4), connected to the first outlet and (35a) a second supply port and (30a) doing.