To provide a folding corner reflector launched into the sky from a launcher, three-dimensionally expanded in the sky, and easily folded and expanded, and having high radar reflecting performance.

This holding corner reflector includes a hollow cylindrical main rod 12 having a concentric hollow hole on its one end 12a, a rod-like sub rod 14 concentrically received in the hollow hole of the main rod and expandable outward along an axis from the one end, a hollow supporting member 16 fixed to one end of the main rod while surrounding the hollow hole, a plurality of rib members 18 attached to the hollow supporting member at inner ends 19a and oscillatable in the expanding direction of the sub rod to an expanding position radially expanded from a folding position positioned at a main rod side, a flexible main cord member 20 connecting an outer end of the sub rod and outer ends of the rib members, and a radio wave reflecting film 22 mounted in a folded state among the main rod, the sub-rod and the rib members, and forming eight corner reflectors on the supporting member 16 as a center at the expanding position.