The emergency diesel generator of a nuclear power plant is a emergency AC power source that starts up within 10 seconds when a LOOP(Loss Of Off-site Power) occurs and supplies power to essential safety facilities. In this study, factors affecting start signal input time, engine rotation start time, 30% of engine rated speed, 80% of engine rated speed were studied to secure starting reliability. As a result, it was found that the section before the 30% of engine rated speed was affected by the mechanical management status from the start signal to the fuel oil linkage system. After the 30% of engine rated speed section, it was the maximum fuel supply section, and the time reduction effect through management improvement was insignificant.