To keep thin the thickness of a packing in a use state by bending a packing body itself so as to be meandered when an outer rib and an inner rib alternately protruding to surface/rear-surface directions are pressed from both sides, related to a water shut-off structure of a fastener.

The packing (40) has: the plate-shaped packing body (41); the outer rib (43) which protrudes from one of the surface and the rear surface of the packing body (41) and surrounds the circumference of a center hole (42); and the inner rib (44) which is located between the outer rib (43) and the center hole (42) and protrudes from the other of the surface and the rear surface of the packing body (41). In a state that an attachment member (retainer 30, for example) and a member to be attached (body 20, for example) are attached between a head (51) and a leg (52), the packings (40, 330 and 430) are compressed and warped between a head (341) and an attachment member (hook 320, for example), or between heads (31, 441) and members to be attached (body 20 and a panel 410, for example), or a member to be attached (panel 310, for example) and the attachment member (hook 320, for example), and thus water is shut off.