A balloon (3) includes: an inflation part (33)； a base end-side cone part (32) and a distal end-side cone part in which the diameter of one end that is connected to the inflation part (33) is larger than the diameter of the other end； and a base end-side leg part (31) and a distal end-side leg part. The base end-side cone part (32) has a first connecting part (321), a second connecting part (322), and a third connecting part (323). A first angle (θ21) between a first line segment (L21) connecting a first point (P21) and a third point (P23) and the extension direction, and a second angle (θ22) between a second line segment (L22) connecting a second point (P22) and a fourth point (P24) and the extension direction, are both larger than a third angle (θ23) between a third line segment (L23) connecting the third point (P23) and the fourth point (P24) and the extension direction.
