To prevent outflow of fuel vapor inside a float chamber from an overflow pipe with certainty.

A fuel discharging port 34a opened upward is formed on an overflow pipe 34 at specified height level inside a float chamber 30. An opening/ closing valve 35 is vertically oscillatably arranged so as to cover the fuel discharging port 34a from the upper side. A portion 35d to be operated is arranged on the opening/closing valve 35 so as to be projected horizontally. A float 32 is vertically moved due to fluctuation of level of stored fuel F inside the float chamber 30 for operating a needle valve (fuel inflow valve) 27. A fuel discharging operation part 32e to be engaged with the operated portion 35d is arranged on the float 32. When the level of the stored fuel F reaches specified height or more, the fuel discharging operation part 32e pushes up the opening/closing valve 35 through the operated portion 35d for opening the fuel discharging port 34a. When the level of the stored fuel F is lowered to the specified level or lower, the fuel discharging operation part 32e is separated from the operated portion 35e to the lower direction, while the fuel discharging port 32e is closed by the opening/closing valve 35.