A gaseous fuel discharge structure is used in a vehicle including an airtight cover disposed within a trunk thereof. The airtight cover covers a gaseous fuel containing tank. The structure includes an air introducing pipe and a gas discharging pipe both connected to the cover. If gaseous fuel leaks from within the tank, the structure is operated to discharge the gaseous fuel out of the vehicle. The air introducing pipe is provided with a fan. The air introducing pipe has an air intake flap while the gas discharging pipe has a discharge flap.