We have been developing a mobility assistive robot with the following concepts [1]: "improved mobility," "health maintenance" and "natural walking appearance." The robot consists of three controls: the free treadmill speed control which allows the user to walk on the treadmill at the desired speed, the driving control which controls the actuators, and the steering control which allows the user to turn using the steering wheel. And this robot to be possible, the most important thing is to develop the alternative treadmill speed control system for older person. The treadmill control system as the interface should be easy and simple because of the older person's characteristics decreasing ability to learn and adjust. Therefore, in this paper, we propose a method of speed control for the treadmill system which enables the user to walk on the treadmill just as they do on the ground. The developed treadmill can detect walking patterns, braking forces, and accelerating forces from the load placed on its DC motors. The treadmill itself cannot detect the user's walking speed, thus we developed a method for converting those input signals into the user's walking speed