These days, robots have been playing a significant role in NASA and JAXA exploration. These explorations provide great scientific return. On mars and lunar surface, there are a lot of loose soil and many steep slopes are found along their crater rims. In such the surface, because of wheels of robot are easy to sink and slip, the wheels of robot can not move forward or backward direction. Therefore, the robots become stuck and do not continue mission. However, in this situation, the wheels of robot can get the bearing force from loose soil. This paper focuses on this bearing force and proposes locomotion method. This study proposes a wheel base length variable mechanism hereinafter known as WB mechanism. WB mechanism uses the bearing force form loose soil. This paper, the first, explains the development of the robot equipped with WB mechanism. Secondly, the experiments of traveling performance are carried out on loose soil. Finally, the traveling performance of each of wheel diameter were discussed. As the results of experiments, the robot equipped with WB mechanism showed high traveling performance. Moreover, we could suggest that the traveling performance can be changed by the wheel diameter.