A fuel tank body has a double-layer structure composed of an inner tank shell and an outer tank shell, so that an inter-tank-shell space is formed therebetween. Because heat of fuel in the fuel tank body is discharged into the inter-tank-shell space, the temperature of fuel in the fuel tank body is prevented from rising. If the pressure in a canister becomes negative due to a negative pressure in an intake system of an engine, more specifically, a negative pressure in a surge tank leading to an air cleaner, high-temperature air in the inter-tank-shell space between the inner tank shell and the outer tank shell flows into the canister. On the other hand, low-temperature air flows from the air cleaner into the inter-tank-shell space which has become negative in pressure.