Medical errors are often occur brought due to complicated combinations of such causes as carelessness of medical workers, troubles of medical appliances, in-appropriate education systems, prolonged working hours, etc. It is quite difficult to remove the risk of medical errors completely, because medical treatment is an action made by human being on another. It is essential to learn positively those examples of medical errors and incidents in order to prevent medical accidents. Since causal factors of medical and industrial accidents have common factors, it seems that analytical methods of accidents for industrial sectors can be also applied to those of medication. The present paper describes how to analyze errors and incidents caused by medical treatment and to establish safety measures against recurrence of the errors and incidents using a technique of Hybrid Analysis of t-m-SHEL Model and RCA (Root Cause Analysis). Results of a case study demonstrate that the newly proposed technique provides us systematic, procedure- and format-based good practice for analyses of medical errors and incidents involving direct, performance shaping and fundamental factors.