Abstract: An object holding structure includes: an inner member including an end surface, a first clamping surface located radially outward of the end surface, and hook portions arranged in a circumferential direction at intervals on the end surface; an outer member located radially outward of the inner member, including an end surface and a second clamping surface opposed to the first clamping surface through an object; a key plate contactable to the end surface and the end surface; and a retaining ring held between the key plate and claw portions of the hook portions. The key plate includes a first ring facing the end surface, a second ring provided radially inward of the hook portions, and inner tabs located between the hook portions and linking the first ring and the second ring.