To provide a fuel shut-off valve 10 which can be closed with high sealing performance even when a float is swung from side to side or inclined relative to the axial direction.

This fuel shut-off valve is provided with a casing 20, and a float mechanism 50 stored in the valve chamber 30S of the casing 20. The float mechanism 50 is provided with a seat member 55 supported by a valve supporting section 53 in the upper part of the float 51. The seat member 55 is formed of a material with flexibility, and is provided with a seat section 55a attached/detached to/from a seal section 31c and curved upwards, a supporting rod 55b protruded in a rod shape downward from the central section of the seat section 55a, and a supported section 55c formed in the lower part of the supporting rod 55b and supported by the valve supporting section 53. The seat section 55a is formed to be deflected with a large deflection margin by the supporting rod 55b relative to the core displacement of the float 51 while maintaining its seated condition onto the seal section 31c.