A shut-off valve for a liquid fuel includes a valve housing in which a float, adapted to bs raised by buoyant force as the liquid fuel flows into the valve housing, and a valve disc, for sealably closing a fuel vapor outflow hole, are arranged in such a manner as to allow the valve disc to be vertically displaceable relative to the float. A plate-like valve member, which carries a rod-shaped protuberance for sealably closing a through hole formed through the valve disc, is disposed between the valve disc and the float. When the float is lowered as the liquid fuel returns from the valve housing to the fuel tank, a first engagement pawl engages the plate-like valve member at a single point and, at the same time, a second engagement pawl engages a flange portion of the valve disc at a single point, whereby the plate-like valve member and the valve disc are opened so as to enable the fuel vapor generated in the fuel tank to flow into a receiving canister. At the time of an occurrence of vehicular accident or emergency, a ball member disposed in the valve housing is slidably displaced along a concave conical surface until the fuel vapor outflow hole is sealably closed by the valve disc via the ball member, thus preventing the liquid fuel from flowing into the canister.