A tube assembly is disclosed which includes an elongated medical tube and a medical elongated body insertable in the medical tube and higher than the medical tube in rigidity and which is used in an assembled state with the medical elongated body inserted in the medical tube to be assembled together. The tube assembly further includes a puncturing section adapted to puncture a living body a dissecting section adapted to dissect the living body as the puncturing section punctures the living body and a rotation restraining section adapted to restrain the medical tube from rotating about its axis in relation to the medical elongated body in the assembled state.
