Our aim is to develop the service robot based on a systematic software engineering method, particularly for real-time, embedded and distributed systems with UML. To do so, we applied the COMET method, which is a UML-based method for the development of concurrent applications, specifically distributed and real-time applications. We describe our experience of applying the COMET/UML method to developing the service robot for the elderly, T-Rot, which is under development at CIR. Here, our emphasis was on an autonomous navigation system for the service robot, which is one of the most challenging issues and is essential in developing service robots, especially mobile service robots to help elderly people. It includes hardware integration for various sensors and actuators as well as software development and integration of modules like a path planner and a localizer.