To surely prevent outflow of fuel to a canister from a tank main body by making a float valve not released even if fuel level surface changes due to turn, acceleration and deceleration of a vehicle.

When a fuel level surface in a tank main body rises and gets close to a full tank level surface, fuel gets over an open upper end of an outer housing 23 and flows into a float housing at a stretch and floats a float 24 in an inner housing 22 to seat the same on a valve seat 14a. Consequently, fuel is prevented from flowing out of the canister via a charge passage 14. Since the float housing 21 has a labyrinth structure keeping communication between an outer housing 23 and the inner housing 2 with a communication hole 22d, fuel level surface in the inner housing goes down and prevents the float 24 from separating from the valve seat 14a, and fuel is surely prevented from flowing out of the canister via the charge passage 14 even if fuel level surface in the tank main body 11 changes due to turn, acceleration and deceleration of the vehicle under this condition.