PROBLEM TO BE SOLVED: To provide a medical device in which a range of an inner diameter of an applicable living body lumen is wide, and it is possible to regulate a flow in the living body lumen and improve performance of removing a material from inside the living body lumen, and a treatment method.SOLUTION: A medical device 10 inserted into a living body lumen for regulating a flow in the living body lumen includes: a shaft part 23； an expansion part 22, which is an elastically deformable tube body having a plurality of gaps 21A, in which the outer diameter in the central part is larger than the outer diameter in the end parts on both sides of the tube body in a natural state in which external force is not applied, and the shaft part 23 is connected to the tube body； a cover part 70 of a cylindrical shape deformable independently from the expansion part 22 while surrounding the outer periphery of the expansion part 22, the two ends of the cylindrical shape being connected to the two ends of the expansion part 22, which can form an overlapped part 78 folded back in an axial direction when the expansion part 22 is expanded； and a sheath 30 that can accommodate the expansion part 22 and the cover part 70.SELECTED DRAWING: Figure 1【課題】適用可能な生体管腔の内径の範囲が広く、生体管腔内の流れを規制して生体管腔内から物質の除去性を向上させることが可能な医療デバイスおよび処置方法を提供する。【解決手段】生体管腔内に挿入されて当該生体管腔内の流れを規制するための医療デバイス１０であって、シャフト部２３と、複数の間隙２１Ａを備えて弾性的に変形可能な管体であり、外力の作用しない自然状態において管体の両側の端部よりも中央部の外径が大きくなり、かつ管体にシャフト部２３が連結された拡張部２２と、拡張部２２の外周を囲みつつ拡張部２２から独立して変形可能であるとともに筒形状を呈し、当該筒形状の両端部が拡張部２２の両端部に連結され、拡張部２２が拡張する際に軸方向に折り返される重なり部７８を形成可能であるカバー部７０と、拡張部２２およびカバー部７０を収容可能なシース３０と、を有する。【選択図】図１
