PURPOSE: To prevent the wear of the one-sided parts of a valve body and a valve seat by positively rotating the body of a float valve utilizing the flow of gasoline flowing into a float chamber.

CONSTITUTION: As the fluid level in a float chamber 19 is lowered with the operation of an engine, a float is lowered causing a lever 14 to move centering around a pin 18, while a lip 20 also to move. Thereby, a valve stem member 38 is lowered in a casing 40, causing a valve body 36 to open up the opening 32 of a valve seat 34. Gasoline enters a float valve device 30 through the opening 32, partly passing through the bypass holes 46 of the casing 40. The diameters d1 to d4 of each of more than one bypass hole 46a to 46d, are made gradually larger in order. And, the valve stem member 38 is made rotate due to the difference in flow rate of gasoline passing through each bypass valve 46a to 46d. Thereby, the valve stem member 38 can be prevented from being one-sidedly worn on any particular side.