Disclosed herein is a back ferrule having a bellows-shaped elastic part. The back ferrule (40) is used, for pipe connection, along with: a connector body (10) having an external thread on an outer circumferential surface thereof; a drive nut (20) having an internal thread on an inner circumferential surface thereof; and a front ferrule (30). The back ferrule (40) includes: a nose part (41) having a front-end inclined surface (41b); a tail part (42) having a rear-end inclined surface (42b); and an outer circumferential surface (43) and an inner circumferential surface (44) connecting the nose part to the tail part. An outer circumferential corrugated surface (45) and an inner circumferential corrugated surface (46) are respectively formed on the outer circumferential surface and the inner circumferential surface between the nose part and the tail part.