A medical device designed to be inserted into a lumen of a living body so as to block a flow of fluid in the lumen of the living body. The medical device includes: a long shaft part； an expandable part； and a covering part. The expandable part is an elastically deformable cylindrical body, and the cylindrical body having a proximal part connected to the shaft part. The covering part takes on a cylindrical shape and is flexible and deformable independently of the expandable part, and the cylindrical shape has a proximal part connected to a proximal part of the expandable part or connected to the shaft part located at a proximal side with respect to the expandable part. The covering part defines a space in the radial direction between a distal side end part of the cylindrical shape and the expandable part.
