It can be performed easily and reliably piercing of the plug body by the body fluid sampling hollow needle, yet the body fluid sampling after the start, it is difficult to occur omission of the body fluid sampling needle from the plug body by the elastic force of the sheath, easily stopper which allows to collect the body fluid to reliably. A plug body for sealing the open end of the body fluid collecting container 14 to be inserted into the holder 11 of the tubular, the plug body 2 which is secured to the open end of the body fluid collecting container 14, the outside of the plug body 2 The holder 11 when a cover member 3 is fitted on the plug body 2 so as to cover the surface, and a side portion 3c covering the outer surface of the plug body 2, the cover member 3 is inserted into the holder 11 are provided on the outer surface of the side portion 3c protrusions 3k which projects radially outwardly of the side portion 3c of the cover member 3 so as to provide frictional resistance in contact with the inner wall of, the plug 1.中空の体液採取針による栓本体への刺通を容易にかつ確実に行うことができ、しかも体液採取開始後には、鞘の弾発力による栓体からの体液採取針の抜けが生じ難く、容易にかつ確実に体液を採取することを可能とする栓体。筒状のホルダー11に挿入される体液採取用容器14の開口端を密閉するための栓体であって、体液採取用容器14の開口端に固定される栓本体2と、栓本体2の外表面を覆うように栓本体2に外装されているカバー部材3とを備え、カバー部材3が、栓本体2の外側面を覆う側面部3cを有し、ホルダー11に挿入された際にホルダー11の内壁と接触して摩擦抵抗を与えるようにカバー部材3の側面部3cの径方向外側に突出している突出部3kが側面部3cの外表面に設けられている、栓体1。
