PROBLEM TO BE SOLVED: To utilize surplus fuel gas generated in a fuel supply line of a main machine as fuel of an auxiliary machine in a fuel supply system of a vessel mounted with a gas-fired two-stroke diesel engine as the main machine.SOLUTION: A fuel supply system 1 comprises: a fuel tank 11 which stores liquefied gas fuel; a fuel gasification device 12 which increases pressure of the liquefied gas fuel and produces fuel gas by gasifying the liquefied gas fuel; main machine fuel supply piping 20 which supplies the fuel gas to an engine 10; a pressure tank 14 which stores surplus fuel gas in the main machine fuel supply piping 20; exhaust piping 31 which connects the main machine fuel supply piping 20 and the pressure tank 14; an exhaust valve device 32 which is installed on the exhaust piping 31; supply piping 33 which connects the pressure tank 14 and at least one auxiliary machine; and a supply valve device 34 which is installed on the supply piping 33. The pressure tank 14 stores the fuel gas at the pr
