In this paper, we proposed a wheel equipped rover with deployable legs that can change the apparent wheel radius in order to improve the runnability of the rover which travels on the ground covered with lunar regolith. Furthermore, we formulated the driving force of the wheel based on Terramechanics and clarified the mechanism of the driving force change using our proposed rover wheel. In addition, the driving force was compared between the original wheel configuration and the leg expanded one in single wheel running experiments, and it was validated that the proposed leg expandable system exhibits higher driving force than the original circular wheel. With this system, in the case of a flat ground surface that does not require a high driving force, the vehicle should use the original wheel state, and when a high driving force is required such like the situation the vehicle need to escape the wheel from the local concaved ground, the proposed expandable leg system can be useful, and then the possibility of traveling on irregular surface efficiently not only on the moon but also on other planets was shown.