To prevent the leakage of liquid which occurs when a load such as vibration and impact of falling is applied to a container housing the liquid during the transportation of the container so that the liquid-backflow preventive function of the container can hardly be maintained.

The length of a backflow preventive material layer between the inside diameter of the maximum circumscribed circle of the liquid container filled with a backflow preventive material corresponding to the wetting height of the backflow preventive material, or the width of the clearance between the inner wall of the container and the outer wall of a float, the tip part of the float and the liquid interface is regulated.