In order to find an effective measure in limited time and budget, it is necessary to judge the priority of the purposes and effects of measures. One important factor s is the degree of risk. We improved FMEA for the risk assessment of human error phenomena, and developed it to a new risk assessment technique. In order to use this technique, sufficient background factors of accidents and incidents need to be analyzed. Moreover, for preventing human errors, not only the error phenomena but also the causative factors should be grasped. We combined the results of assessing the risk of error phenomena with causes of errors, to create a method of managing and preventing human errors which could be adopted in a railroad office.