In order to avoid a sudden cardiac death by a fatal arrhythmia, various living body information for generating a signal which shows a level of an autonomic tone is detected by a sensor or a VT/VF risk event is detected so as to control the stimulation of the vagus nerve or the nerve stimulation waveform. For this purpose, the parameter of the nerve stimulation signal is controlled according to a detection of the living body information represented by a QT interval which is measured by intracardiac information of the heart or a detection of a VT/VF risk event represented by a ventricular premature contraction which is picked up from spontaneous cardiac events.