An intracardiac defibrillation catheter system equipped with a defibrillation catheter, a power source device and an electrocardiograph. The defibrillation catheter is equipped with a first DC electrode group and a second DC electrode group. The power source device is equipped with a DC power source unit, a catheter-connected connector, an electrocardiograph-connected connector, an arithmetic processing unit, which controls the DC power source unit and has an output circuit for outputting a direct current voltage from the DC power source unit, and a changeover unit, in which the catheter-connected connector is connected to a common contact. The electrocardiograph-connected connector is connected to a first contact, and the arithmetic processing unit is connected to a second contact. In the intracardiac defibrillation catheter system, electric energy necessary and sufficient for defibrillation can be surely supplied. The defibrillation catheter can be used as an electrode catheter for cardiac potential measurement when a defibrillation treatment is not performed.
