A cooling unit is mounted to an upper wall of a fuel tank so as to cool fuel. A control valve and a vent valve are disposed in a vapor line extending from a float valve to a canister. The control valve and the vent valve are disposed in parallel with one another and constitute a valve member. A cooling unit is mounted to an evaporation passage between a float valve and the valve member. Operation of the cooling units serves to cool fuel and inhibit generation of vapor. If the pressure in the fuel tank exceeds a control pressure, a control circuit opens the control valve and performs control such that the pressure in the fuel tank becomes lower than a running-state relief pressure.