CONTAINER LID CONFIGURED FROM BOTH INSIDE PLUG AND LID BODY

A container lid is composed of a synthetic resin inside plug (2) to be mounted on the mouth neck of a container, and a synthetic resin lid body (4) to be mounted on the inside plug. A breakable thin-walled line (18) formed in a closing wall of the inside plug is of a shape having an outer arcuate portion (18b) extending from a breakage start end portion (18a), and an inner arcuate portion (18c) extending from the breakage start end portion, and defines an arcuate deformation region (20). A locked means (22) is annexed to the deformation region, and a locking means (58) is disposed in the lid body. When the lid body is rotated in a predetermined direction relative to the inside plug, the locking means is locked to the locked means. When the lid body is rotated further in the predetermined direction relative to the inside plug, a force is exerted on the deformation region via the locking means and the locked means, so that the breakable thin-walled line of the inside plug is broken and the deformation region is deformed, whereby a pass-through opening (90) is formed in the closing wall (6) of the inside plug.