An expansion device is disclosed, which includes an outer tube in which a plurality of wire portions extending along an axial direction are disposed so as to be arranged in a circumferential direction in the vicinity of a distal portion, and an inner tube that is inserted into the outer tube and is interlocked with the distal portion of the outer tube. The wire portion has an expansion portion which expands radially outward when the outer tube is compressed in the axial direction, a distal side fragile portion which is formed on the distal side of the expansion portion and has flexural rigidity lower than that of the expansion portion, and a proximal side fragile portion which is formed on the proximal side of the expansion portion and having flexural rigidity lower than that of the expansion portion.
