To reduce an unfavorable molding of a cap which can be classifiably recovered, and prevent the gripping tab from being carelessly cut at the classifying recovery time by forming a pair of scores at symmetrical locations on the right and the left from a pair of tear starting end sections on the right and the left, and arranging a score non-formed section between tear final end sections along respective scores.

Respective tear starting end sections 11A and 11B are arranged in a manner to be in contact with a pair of right and left slit windows 17A and 17B, and a pair of thinner scores 8A and 8B are formed in a manner to be symmetrical on the right and the left from the tear starting ends sections 11A and 11B along respective shoulder sections 4A and 4B of a fitting external cylinder. At the same time, a score non-formed section 9 is arranged between respective tear final ends 12A and 12b along the thinner scores 8A and 8B. Then, on the outside of the vicinities of respective tear starting end sections 11A and 11B, respective gripping tabs 20A and 20N are integrally formed, and also, the lower ends of respective slit windows 17A and 17B are connected to respective weakened descending lines 19A and 19B. When this internal plug 6 is recovered, respective gripping tabs 20A and 20B are pinched and pulled outward, and respective tear sections are torn. Then, the internal plug 6 is pulled up by holding respective cut-off pieces and the score non-formed section 9.