To easily and securely fix a metal cap to a bag.

An aperture edge of a bag main body part is inserted into a groove part 11 of a metal cap 10. After this, part of an inner wall surface of the groove part 11 of the metal cap 10 is protruded inward by providing a claw part 14 and bending it, for example, to press an inserted part of the bag main body part onto an inner wall surface of the other by a protruded part as a tip part of the claw part 14, thereby the bag main body part is fixed into the groove part 11.