On the basis of the report published from Marine Accident Inquiry Agency, the operating state of the safety devices i.e. the alarm and automated shut-down device for engine system when the engine troubles arose was investigated. Results showed that the cases in which the engine broke down were 42 (25%), even though the safety devices operated, the cases in which the engine broke down were 67 (39%), since they did not operate.The breakdowns of the former causes in the engine troubles were artificial mistake, insufficient inspection, non-operation of engine shut-down device and the latter causes were insufficient maintenance, un-installation of the safety device, sensor fault. Therefore, the following matters are recommended from the viewpoint which prevents the engine troubles, 1) the execution of the operating test of the safety device, 2) the execution of the stop of the engine by the emergency stop button.