A retainer structure having excellent workability of attaching to and removing from a panel is obtained. In an approximately cylindrical retainer main body (22), a cap holding portion (26) for attaching a cap (18) which is an attached member, and a panel clamping piece (32) contacting a body panel (14) from a side opposite to a seal packing (20) so as to clamp the body panel (14) between the panel clamping piece and a flange portion (24), are formed. The cap holding portion (26) and the panel clamping piece (32) are formed at positions different in a circumferential direction of the retainer main body (22).