The intracardiac defibrillating catheter is provided with a catheter tube (10), a handle (20), a first DC electrode group (31G), and a second DC electrode group (32G)； and performs defibrillation inside the heart by applying voltages of mutually differing polarities on the first DC electrode group (31G) and the second DC electrode group (32G). At the front end region of the catheter tube (10) are formed a first curved part (101), obtained by curving the front end whereon the first DC electrode group (31G) is mounted, and a second S-shaped curved part (103) on the base side of the second DC electrode group (32G) and on a plane that is orthogonal to the plane that contains the first curved part. The curved shape of the first curved part (101) is changed by manipulation of the handle (20). When inserted into the heart, the defibrillating catheter is able to introduce the front end easily into the opening of the coronary sinus that is in the inner wall of the right atrium and after insertion, to bring the electrode groups into contact with or in close proximity to the anterior inner wall of the right atrium.
