Using NIM-Eclipse monitoring instrument (Medtronic), we will check action potential of cavernous nerve, bulbocavernosus reflex and pudendal nerve somatosensory evoked potential in real time during robot assisted laparoscopic radical prostatectomy for preservation of erectile function. In this feasibility and protocol setting phase I/II study, we will evaluate the safety and efficacy of pelvic autonomic nerve monitoring and mapping using NIM-Eclipse monitoring instrument.