To obtain efficiently a gas turbine fuel which does not evolve CO<SB POS="POST">2</SB> during combustion by reforming liquefied natural gas successively in a reformer and by the shift reaction, separating CO<SB POS="POST">2</SB> from the reformed gas, and liquefying the CO<SB POS="POST">2</SB> by the cold heat of the liquefied natural gas. CONSTITUTION: After the recovery of the cold heat of liquefied natural gas (hereinafter referred to an LNG) in cold-heat-recovery heat-exchangers 1 and 2, the LNG is gasified in an LNG vaporizer 3 and fed to a reformer 4. Steam is fed to the reformer 4 at the same time to reform CH<SB POS="POST">4</SB> in the feed gas to H<SB POS="POST">2</SB> and CO. Then, the reformed gas is introduced into a high-temperature CO shift reactor 5 and a low-temperature shift reactor 6 to reform the CO through the shift reaction with steam to H<SB POS="POST">2</SB> and CO<SB POS="POST">2</SB>. Thereafter, the reformed gas is fed into PSA11 for CO<SB POS="POST">2</SB> absorption to separate and remove the CO<SB POS="POST">2</SB> which is then liquefied in a CO<SB POS="POST">2</SB> liquefier 13 making use of the cold heat of the LNG. On the other hand, the reformed gas, from which CO<SB POS="POST">2</SB> has been separated, is used as a fuel in a gas turbine 15.