A fuel cutoff valve of the invention includes a casing body having a valve chamber and a holder element, a float having a seat member on its top, a movable valve element that is fitted in the holder element in a vertically movable manner, and a first connection conduit and a second connection conduit that connect inside of the valve chamber with outside. When the fuel level in a fuel tank rises to a preset first fluid level, the float moves up to shut off the first connection conduit. When the fuel level further rises to a preset second fluid level, the float further moves up to press the movable valve element up and shut off the second connection conduit. The fuel cutoff valve of this simple structure effectively prevents a blowing back flow of fuel in the course of fuel supply without requiring any subtle setting of a spring load.