PURPOSE: To improve the opening/sealing property of a composite cover constitut ed of an intermediate plug, an inner cover, and an outer cover by forming a pair of weak lines ruptured when a grip piece is pulled on the inner cover made of a metal thin plate, and sticking a sealing protruded stripe provided on the inner face of the outer cover in the inside region of the weak lines.

CONSTITUTION: A composite cover applied to the bore section 4 of a medicinal liquid container is constituted of an intermediate plug 8, an inner cover 10, and an outer cover 12. The intermediate plug 8 has a circular main section 14 and a cylindrical trail section 16, and the trail section 16 is inserted into the bore section 4. The inner cover 10 is made of a metal thin plate and has a circular top face wall 22 formed with a circular opening 26 at the center and a cylindrical skirt wall 24, a grip piece 28 is protruded from the lower end of the skirt wall 24, and a pair of weak lines 30, 32 are formed on both sides of the grip piece 28. The outer cover 12 is made of a synthetic resin and has a circular top face wall 34 and a cylindrical skirt wall 36, and it is stuck to the top face wall 22 of the inner cover 10 at a circular sealing protruded stripe 38 on the inner face of the top face wall 34.