To provide a balloon catheter for electrically isolating a pulmonary vein capable of forming a wall penetrating necrosis layer around a pulmonary vein opening without excessively igniting an endocardial membrane and individually igniting four pulmonary vein openings one by one.

The balloon catheter for electrically isolating a pulmonary vein comprises a catheter shaft consisting of a catheter outer cylinder shaft 2 and a catheter inner cylinder shaft 6, a balloon 4 having a shaft capable of loop contact with a predetermined portion of the single pulmonary vein opening 20 in an expanded state, a high frequency current-carrying electrode 8 arranged in the wall of the balloon or in the balloon for transferring high frequency power to a counter electrode arranged on a body surface, a lead wire 12 to be electrically connected to the high frequency current-carrying electrode 8, cooling means 38 for irrigating the catheter shaft and the balloon 4 to be cooled with a cooling water 36, and a temperature sensor 14 capable of monitoring a temperature in the balloon.