Services that operate normally, independently, will behave differently when simultaneously initiated with another service. This behavior is called a feature interaction. A feature interaction, where the next state can not be determined uniquely for one event, is called a non-determinacy feature interaction. To detect the interaction, judgment has to be made as to whether the state, where the non-determinacy occurs, is reachable from the initial state or not. For the judgment, many methods have been proposed. But, still now, it is required huge computation time to judge the reachability. This paper proposes a new method to test the reachability using a little knowledge elicited beforehand. By using the proposed method computation time was reduced drastically. Besides, by applying the proposed method to a benchmark, the proposed method was confirmed to be effective and reasonable.