The purpose of the present invention is to provide an in vivo indwelling member which, while having a shape that curves in various directions in a complex manner and that can expand easily inside of an aneurysm, etc., assumes a state in close contact with the inner wall of the aneurysm, etc., preventing dislodgment, and can further improve indwelling density and maintain excellent operability; and to provide an in vivo indwelling member placement device provided with said in vivo indwelling member. The shapes of two or more three-dimensional units (a medium three-dimensional body 4A and a large three-dimensional body 4B) are provided on a primary coil (11), so each three-dimensional unit is configured by a continuous arrangement of at least four shape sites (51a-51e/52a-52f) across four planes, and the normal directions of the four planes are all in a relation perpendicular to the direction of a prescribed common axis (a1/a2), and said at least four curved shape areas (51a-51e/52a-52f) are formed in one of the planes of an imaginary cylindrical body having a quadrilateral shape when seen from the common axis (a1/a2), which is surrounded by the four planes.La présente invention vise à fournir un élément à demeure in vivo qui, tout en ayant une forme qui se courbe dans diverses directions de manière complexe et qui peut s'étendre facilement à l'intérieur d'un anévrisme, etc., adopte un état en contact étroit avec la paroi interne de l'anévrisme, etc., empêchant un délogement, et peut en outre améliorer la densité à demeure et conserver une excellente exploitabilité ; et à fournir un dispositif de placement d'élément à demeure in vivo comprenant ledit élément à demeure in vivo. Les formes d'au moins deux unités tridimensionnelles (un corps tridimensionnel moyen 4A et un grand corps tridimensionnel 4B) se trouvent sur une bobine primaire (11), de telle sorte que chaque unité tridimensionnelle est configurée par un agencement continu d'au moins quatre sites de forme (51a