A steam reformer generates reformed gas by a steam-reforming reaction of hydrocarbon gas such as natural gas. A methanol synthesis column and a gasoline synthesis column synthesize gasoline from the reformed gas via methanol and produce a liquid fuel. A superheater superheats a part of low-pressure steam that has been heat-recovered from the reformed gas with a part of middle-pressure steam that has been heat-recovered by the methanol synthesis column or the gasoline synthesis column, and the steam thereby brought into an unsaturated state is supplied to a low-pressure steam turbine.