A fuel cutoff valve 10 has a float assembly 52 and an upper valve plug 60 located in a valve chest 30S defined by a casing 20. The float assembly 52 has a valve support member 55 formed in its upper portion to support the upper valve plug 60. The upper valve plug 60 has a support convex 66b held on a support plane 56a of the valve support member 55, where a center of gravity of the upper valve plug 60 is located below a supporting point 55a around which the support convex 66b is balanced on the valve support member 55. The upper valve plug 60 includes a first valve section 61 and a second valve section 65. The first valve section 61 has a first valve body 62 and a sheet member 64. The first valve body 62 is made of POM (polyoxymethylene), while the second valve section 65 is made of PA6 (polyamide) containing 30% of glass fibers. The second valve section 65 is accordingly structured to have a lower density than the first valve body 62. This arrangement ensures the excellent sealing property even in the event of vibration of the fuel cutoff valve 10 submerged in the liquid fuel by inclination of the vehicle body.