Requirement specifications written in natural language might cause miscommunication among developers depending on how they are understood. Without removing any ambiguities, we cannot construct systems satisfying the need for software safety. Removing ambiguities should be performed in early steps during the development. In this paper, Requirement Analysis Support Tool (RAST) will be introduced. RAST system analyzes requirement specifications based on linguistic information. By using RAST system, we can expect that requirement engineers can communicate with each other in common notations, and use logical expressions rather than using requirement specifications written in natural language.