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 6 includes a contact portion 11 that is to contact a target site A and a noncontact portion 12 that is not to contact the target site A. A membrane thickness of the contact portion 11 is thinner than that of the noncontact portion 12. Then, the target site A that is in contact with the thin contact portion 11 is selectively ablated, while making heat leak from the thick noncontact portion 12 less likely to occur. Hence, only the target portion can be efficiently ablated.
