PURPOSE: To obtain a large valve opening force by guiding a cylindrical or conical float in the vertical direction to be disposed in a valve chest and installing a lever having a valve element in the valve chest with a gradient of an acute angle to the displacement of the float.

CONSTITUTION: A float 11 formed like a cylinder or a cone is guided in the vertical direction and disposed in a valve chest 4. A lever 13 having a valve element 15 for opening and closing a valve opening 9 is installed in the valve chest 4 with a gradient of an acute angle with respect to displacement in the valve opening direction of the float 11. The float 11 is guided by a guide means 6, displaced in the vertical direction with the liquid level in the valve chest 4 and brought into contact with the lever 13. As the lever 13 is inclined at an acute angle, buoyancy or dead load of the float 11 works on the lever as a wedge force to increase the valve opening force. Thus, the inclination of the float will not cause a change of contacting position with the lever so as to keep a large valve opening force.