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.