To uniformly heat a balloon as a whole.

A high frequency heating electrode 3 and a temperature sensor 4 are disposed within the balloon 2 attached to a tip of a catheter body 1. With the balloon 2 abutting an opening 12a of the pulmonary vein, heating liquid in the balloon 2 is heated by the electrode 3 whereby the opening 12a of the pulmonary vein is cauterized in a ring shape. A reservoir 41 is connected to a connector 20 connected to the rear end of the catheter body 1. The diaphragm 42 of the reservoir 41 is driven by a motor 43 to reciprocate to thereby vibrate heating liquid in the reservoir 41, with this vibration being transmitted to the heating liquid in the balloon 2 via heating liquid in the connector 20 and heating liquid in the catheter body 1. The high-temperature heating liquid heated by the heating electrode 3 tends to rise and collect in the upper part of the balloon 2, but since the heating liquid in the balloon 2 is stirred by the vibration, the balloon 2 is uniformly heated as a whole.