A screw expander
system includes a screw expander provided with an expansion space for expanding an operating medium, an operating medium inlet, an operating medium outlet, oil inlets, and oil outlets, a condenser which condenses a mixture, sent from the screw expander, of oil and the operating medium, a pump which pressure-feeds the mixture sent from the condenser, and an
evaporator which evaporates the operating medium contained in the mixture. The screw expander
system circulates and supplies the operating medium sent from the
evaporator, to the operating medium inlet, and circulates and supplies the oil sent from the
evaporator, to the oil inlets. An oil separating tank which separates the mixture into the operating medium and the oil is disposed between the evaporator and the screw expander, and an oil containing section of the oil separating tank and the oil inlets of the screw expander are connected.