To eliminate the need for enlarging a water tank, easily mount a valve, greatly reduce costs and ensure a relationship between the up-and-down movement of a float according to a variation of water level and an opening of a valve.

This float valve has a pantograph-type link mechanism 9 for opening and closing a valve 3 provided on the tip end of a flow-in pipe joined to a water tank 1 according to the up-and-down movement of a float 8, a cylinder 28 extended downward from a support frame 16 of a joint of the upper ends of the upper driven arms 18c, 18d of the pantograph-type link mechanism 9 and a float shaft 8a, and a guide member 29 which crosses the pantograph- type link mechanism 9 and extends upward from a support frame 17 for rotatably supporting the crossing part thereof and is fitted in a cylinder 28 such that it can be slid up and down, whereby the float 8 is guided straight up and down by a variation in water level of the water tank 1.