This paper proposes a new reliability measure, its mathematical formulation, and evaluation algorithm to be used in reliability design of communications networks. End-to-end reliability, which was traditional reliability measure, has become irrational because it assumed that telephone was common service of communications networks while today’s main services are multi-users and area-wide services such as TV conference. Another reason to claim traditional measure arises from the reality of maintenance. Maintenance section in communications networks is responsible for its maintenance-area where various paths go through; not only Tokyo-Osaka but also Sendai-Fukuoka and other pairs must be cared. That is, failures causing the stop of any pair in the maintenance-area are serious for maintenance section. Now, our proposed measure can solve these irrationalities.