PURPOSE: To prevent firmly excessive dropping down of pressing force of a sealing member for the mouth part when applied with a load on the upper surface of a lid, so that defective sealing can be surely avoided by forming a part of a skirt wall of non-foamed plastic having a specified elasticity.

CONSTITUTION: A body 4 having a ceiling wall 8 and a skirt wall 10 is formed of ordinary non-foamed plastic having an elasticity of more than 5000kg/cm2 and the skirt wall 10 includes a high elasticity part 18 of an elasticity of 1000 to 3000kg/cm2. When a load is applied on the up[per surface of a container lid, the high elasticity part 18 is force to decline the skirt wall 10 positively inward in a radial direction and downward by a recovering force, while the container lid itself is kept moved slightly downward, so that an upper side surface of a female screw thread 14 of the skirt wall 10 is brought into contact with a lower side surface of a male screw thread of a mouth part 22. Accordingly, when the movable load is removed, the body 4 is prevented from rising up and a dropdwon of the pressing force of a sealing member 6 for the top surface of the mouth part 22 can be prevented.