A cover includes an inner rib structure, an outer rib structure and an elastic structure. The inner rib structure is a tube-shape having a first end portion and a second end portion in an axial direction and has a flange formed on the second end portion and protruded toward radial direction. The outer rib structure has the first end portion and the second end portion formed along the axial direction, is a tube-shape covering an outer periphery of the inner rib structure, has an outer rib fastener formed on the first end portion, and has a cover portion formed on the second end portion and covering an outer periphery of the flange. The elastic structure is clamped between the outer rib fastener of the outer rib structure and the first end portion of the inner rib structure and is plugged the first end portion of the inner rib portion. A gap is between the cover portion of the outer rib structure and the flange of the inner rib structure, and the gap is open in the second end portion of the outer rib structure in the axial direction.蓋體包括內肋構件、外肋構件及彈性構件。內肋構件形成為在軸方向具有第一端部及第二端部之筒狀,而在第二端部側形成往徑方向突出之法蘭部。外肋構件形成為在軸方向具有第一端部及第二端部、且可被覆內肋構件的外周的筒狀,在第一端部形成有外肋卡合部,並且在第二端部形成有覆蓋法蘭部的外周之遮覆部。彈性構件為挾設在外肋構件的外肋卡合部與內肋構件的第一端部之間並填塞內肋構件之第一端部。在外肋構件的遮覆部與內肋構件的法蘭部之間形成有空隙,而空隙在外肋構件的第二端部側於軸方向開放。1‧‧‧內肋構件2‧‧‧外肋部材3‧‧‧彈性構件4‧‧‧封閉構件10‧‧‧蓋體11、21‧‧‧本體部12‧‧‧法蘭部13‧‧‧薄膜20‧‧‧輸液袋(容器本體)22‧‧‧遮覆部30‧‧‧埠口31、32、121‧‧‧溝111‧‧‧上端部211‧‧‧突出部212‧‧‧外肋卡合部s‧‧‧空隙
