An intracardiac defibrillation catheter system equipped with a defibrillation catheter 100, a power source device 700 and an electrocardiograph 800. The defibrillation catheter 100 is equipped with a first DC electrode group 31G and a second DC electrode group 32G the power source device 700 is equipped with a DC power source unit 71, a catheter-connected connector 72, an electrocardiograph-connected connector 73, an arithmetic processing unit 75 which controls the DC power source unit 71 and has an output circuit 751 for outputting a direct current voltage from the DC power source unit 71, and a changeover unit 76 in which the catheter-connected connector 72 is connected to a common contact, the electrocardiograph-connected connector 73 is connected to a first contact, and the arithmetic processing unit 75 is connected to a second contact. According to this intracardiac defibrillation catheter system, electric energy necessary and sufficient for defibrillation can be surely supplied, and the defibrillation catheter 100 can be used as an electrode catheter for cardiac potential measurement when no defibrillation treatment is performed.
