An insertion guide tube that is inserted into a sealing case and that houses a blockage bag in a reduced-size state can be moved inside the sealing case and inside a branch pipe portion along an axis of the branch pipe portion until the insertion guide tube is brought into an abutting position in which at least a part of a leading end portion of the insertion guide tube abuts against an outer surface-side peripheral edge portion of a branch port on an outer circumferential surface of a fluid pipe. In a state in which the blockage bag is located at a predetermined internal flow passage blocking position, an axis adjustment portion that can make sliding contact with an inner surface of the insertion guide tube is located in a portion corresponding to branch port in a radial direction of the fluid pipe.