PURPOSE: To improve the total efficiency by coupling a gas turbine using liquidized gas as fuel, Rankine cycle turbine and a small generator through a clutch while condensing the exhaust gas from Rankine cycle turbine through liquidized gas.

CONSTITUTION: LNG fed from LNG tank 1 and boosted by a pump 2 will enter into a condenser 3 to condense the exhaust gas from Rankine cycle turbine A employing low boiling point intermediate medium. LNG from a control valve 4 is evaporated in LNG evaporator 8 and enter into a combustor 5. While the condensed intermediate medium is boosted by a pump 9 and enter into a turbine A to perform a work. Upon start of turbine the clutch 17 is coupled while upon completion of start the clutch 11 is coupled. Consequently a starter is not required while the cooling heat of LNG can be utilized effectively.