A straightening device including: a plurality of rolling members, defining a first channel which is configured for a tubular member to pass therethrough, an extending direction of the first channel being transverse to at least one extending direction of at least one pivot of at least one of the rolling members; at least three shells, each of the at least three shells including two arm portions which are transversely connected with each other, the plurality of rolling members being rotatably disposed between the arm portions, at least one side of at least one of the arm portions having a protruding wall, the protruding wall extending along the at least one extending direction of the at least one pivot and being at least partially overlapped with at least one of the plurality of rolling members as viewed in a radial direction of the at least one pivot.