To provide a fuel level-responsive valve that solves conventional defects by using an elastically sealing valve member capable of a lever type opening action, and a valve opening and closing method therefor.

The fuel level-responsive valve 16 comprises the valve member 25 brought into sealing contact with a vent outlet 32 of vapor gas, and has a float 24 movable to pull the valve member off the vent outlet when a fuel level drops. The valve member 25 has a thin and flexible seal portion 26 for engaging the vent outlet with small sealing force, and a hard circumferential portion 27 operated by a rigid cage 33 or frame connected to the float 24. When the float 24 drops, the cage 33 is brought into contact with the hard circumferential portion 27 to lever the valve member 25 off the vent outlet 32.