There is provided a balloon catheter system, enabling 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. A balloon includes a contact portion that is to contact a target site and a noncontact portion that is not to contact the target site. A membrane thickness of the contact portion is thinner than that of the noncontact portion. Then, the target site that is in contact with the thin contact portion is selectively ablated, while making heat leak from the thick noncontact portion less likely to occur. Hence, only the target portion can be efficiently ablated.
