In future lunar/planetary exploration missions, wheeled rovers will be promising robots to perform wide-area explorations. Wheeled robots, however, are prone to slip in soft and uneven terrain, and therefore, securing the mobility performance is a critical problem. This paper first describes a simple soil-wheel interaction model which enables slipratio estimation from a combination of wheel load and traction. Second, a drive control method for maintaining vehicle mobility is discussed and a six-wheeled robot which implements the control system was developed. The robot has six wheels and six vertical suspensions with built-in linear actuators. Load cells are installed between each wheel and suspension to monitor the wheel load, and the positions of wheels are individually controlled by moving the suspensions up and/or down so as to keep the desired wheel loads. In this study, a simple algorithm for distributing equivalent load to every wheel was implemented in the control system. Experiments were performed and the effectiveness of the drive control method was examined.