Provided are a medical device and a treatment method with which it is possible to effectively remove objects flowing within a biological lumen while reducing the burden on a living subject. This medical device (1) is inserted within a blood vessel and used for capturing a blood clot (300) within said blood vessel, said medical device (1) comprising: a long shaft portion (24)； an expansion portion (20) that is an elastically deformable cylinder including a plurality of spaces (21A), and is connected to the shaft portion (24)； and a flexibly deformable closed portion (70) that is partially disposed on the expansion portion (20) so as to close off the spaces (21A) of the expansion portion (20). In a folded state in which the expansion portion (20) is folded over in the axial direction such that a proximal site of the expansion portion (20) approaches a distal site of the expansion portion (20), a flow passage through which a fluid can pass is formed between an outer portion (22) that is located on the outer side of the expansion portion (20) in the radial direction and an inner portion (22A) that is located on the inner side of the expansion portion (20) in the radial direction and includes the closed portion (70).L'invention concerne un dispositif médical et une méthode de traitement avec lesquels il est possible d'éliminer efficacement des objets s'écoulant à l'intérieur d'une lumière biologique tout en réduisant la charge sur un sujet vivant. Ce dispositif médical (1) est inséré à l'intérieur d'un vaisseau sanguin et est utilisé pour capturer un caillot sanguin (300) à l'intérieur dudit vaisseau sanguin, ledit dispositif médical (1) comprenant : une partie d'axe long (24)； une partie d'expansion (20) qui est un cylindre élastiquement déformable comprenant une pluralité d'espaces (21A), et qui est reliée à la partie d'axe (24)； et une partie fermée déformable de manière flexible (70) qui est partiellement disposée sur la partie d'expansion (20) de façon à fermer les
