A balloon catheter system enables only a target site to be efficiently ablated, ensuring a balloon to be able to be brought into close contact with the target site in conformity to a shape of the target site. The balloon includes a contact portion that contacts the target site and a noncontact portion that does not contact the target site. A membrane thickness of the contact portion is thinner than that of the noncontact portion The target site that is in contact with the thin contact portion is selectively ablated, while the thick noncontact portion is less likely to exhibit a temperature increase. Hence, only the target portion is efficiently ablated.
