Numerous scenarios have been developed in order to create visions of a sustainable society, such as the IPCC's Scenarios. However, sufficient computational assistance has not been provided for designing scenarios. One critical problem is that it is difficult to understand scenarios rationally since scenarios are written in a text form and their logical structure is unclear. For supporting computer-aided scenario design, this paper presents the concept of Sustainable Society Scenario (3S) Simulator. The key approach is to structure scenarios for computerizing them by representing a scenario structure as a directed graph. Based on this approach, this paper proposes a method for dynamically connecting scenarios with associated simulators for their reuse. A case study illustrates that our method clarifies the logical structure of a scenario, e.g., clarifying rationales for deriving conclusions. Also, the method succeeds in exploring alternative futures by changing assumptions in the scenario.