The fuel cutoff valve includes a casing and a float mechanism. The float mechanism is composed of an outside float and an inside float. The outside float includes an outside float body of round tubular shape having a float chamber that connects with a valve chamber via a through-hole formed in its upper part; and an outside valve portion disposed on the upper part of the outside float body and adapted to open and close an outside connecting passage. The inside float has an inside float body accommodated and adapted to rise and fall within the float chamber, and an inside valve portion disposed on the upper part of the inside float body and adapted to open and close the inside connecting passage through the through-hole.