PROBLEM TO BE SOLVED: To provide an expansion device capable of uniformly expanding a wide range of an expansion part, while reducing a burden applied to a living body.SOLUTION: An expansion device 1 includes an outer tube 4 in which a plurality of linear materials 47 extending along the axial direction, near a distal end thereof and an inner tube 2 inserted into the interior of the outer tube 4 and connected to the distal end of the outer tube 4. Each linear material 47 includes: an expansion part 44 expanding outward in the radial direction by compression of the outer tube 4 in the axial direction a distal-side vulnerable portion 45 formed at a distal side of the expansion part 44 and having bending rigidity lower than that of the expansion part 44 and a proximal-side vulnerable portion 46 formed at a proximal side of the expansion part 44 and having bending rigidity lower than that of the expansion part 44.
