In recent years, the RAMS (reliability, availability, maintainability and safety) international standards have been established, and emphasis has come to be placed on availability as well as safety more than ever before. Accordingly, in order to ensure the targeted availability of railway signalling systems, the authors studied a method of applying measures to such systems from the viewpoint of availability. The results confirmed that it is possible to identify effective measures applicable to the individual pieces of equipment that constitute these systems to attain target values. They also verified the effectiveness of the evaluation method, which involves recognition of status, setting of target values and determination of applicable measures to attain target availability.