To achieve a constitution of hardly closing a valve, even if there is a large flow of fuel vapor to an external part from the inside of a fuel tank, in a fuel cutoff valve.

The fuel cutoff valve 10 includes: a casing 20 forming a valve chamber 20S; a first valve mechanism 50 having a float 51; and a second valve mechanism 60 arranged under the float 51 and opening and closing an introducing port 37 Pa connected to the valve chamber 20S. The second valve mechanism 60 includes a valve plate 61 installed in an opening peripheral edge part of the introducing port 37a of the casing 20 and formed of a metallic thin plate, and is constituted so that a closing body 62 of receiving an air current of turning toward the fuel cutoff valve 10 from the inside of the fuel tank FT, performs valve-closing operation for reducing the opening area of the introducing port 37 Pa.