The fuel cutoff valve comprises a valve support on the upper part of the float, and the seat member is mounted on the valve support. The valve support has the bending space that has an inner diameter larger than the outer diameter of the seal part. The seat member is formed from a rubber material, has a side wall formed in a cylindrical shape from the outer periphery of the seat part and a stopper on the side wall, forming the mounting space by being formed in an almost a rectangle shape cross section, and being supported on the valve support by fitting the valve support on the mounting space. The seat part is elastically deformed in the bending space direction when set on the seal part and closes the connection path.