We propose a new algorithm for obstacle negotiation of a mobile robot known as a variable single-tracked robot (VSTR). The robot was originally designed for the purpose of rescue operations hence, its ability to traverse various environments Should be guaranteed. Previous experiments have already shown that the special structural characteristics of a VSTR enable it to easily climb indoor stairs. However, the VSTR has a critical drawback in that all of its functions are realized by an operator and the robot cannot detect obstacles or transform its driving mode by itself. For this reason, we have enhanced the system with the basis for autonomous navigation, i.e., the ability to negotiate obstacles, and we have introduced a methodology for practical Use. Our experiments Confirm that the driving mode decision, which is controlled by position-sensitive detector infrared sensors, gives decisive improvement. Moreover, the experimental results show that the robot can overcome several obstacles, thereby reflecting the benefits of the proposed algorithm. (C) Koninklijke Brill NV, Leiden and The Robotics Society of Japan, 2008