To prevent discharge of cooling discharge water to sea, to prevent the occurrence of closure of a piping owing to adhesion and growth of organisms on a pipe wall, further to suppress corrosion of a heat transfer pipe, and additionally to prevent lowering of a combustion gas turbine output owing to the increase of an atmospheric temperature during a summer season. CONSTITUTION: A steam turbine 62 mechanism is provided with a condenser 63 mechanism to restore steam after use to water. A carburetor 1 is provided to heat-exchange Liquefied natural gas 1a fed from the outside of a system with a first heating medium 1b circulating a first circulation route L1 formed in the system to gasify the liquefied natural gas 1a into natural gas 1a' for fuel. A first heat-exchanger 41 is located in a first circulation route L1. A second circulation route L5 through which a second heating medium if is circulated is formed between the first heat-exchanger 41 and the condenser 63 and heat-exchange of steam 1d fed to the condenser 63 trough the second heating medium 1f with the first heating medium 1b fed to the second heat-exchanger 41 is practicable.