A segment is coupled to additional segments to constitute a rehabilitating pipe for repairing an existing pipe. The segment comprises an inner plate that defines the inner circumferential surface of the rehabilitating pipe and has an opening therein for performing the work of mutually coupling the segments in the circumferential direction of the rehabilitating pipe, and a cover that is fitted into the opening from the bottom surface side of the inner plate. To fix the cover to the inner plate, the cover is provided with a projection and with an engaging member that is movable between non-engaging and engaging positions. The cover is fitted into the opening with the projection into engagement with the inner plate on one side edge of the opening and the engaging member is then brought into engagement with the inner plate on the other side edge thereof, thereby fixing the cover to the inner plate to plug the opening thereof.