People having severe cerebral palsy cannot move by themselves due to physical limitation of their limbs. This always constitutes a great handicap for them. The purpose of our work is to facilitate independent movement for such people. We developed an electric powered wheelchair for a severely disabled cerebral-palsied girl. Although she cannot control her limbs, she can move her head as she intends. Measurement of her three-dimensional head movements indicated that she can rotate and flex her neck very well. As a result, her rotation angle and flexion angle were adopted as the controlling parameters. This system consisted of a three-dimensional position and angle sensor (ISOTRAK system), head operating start switches, an emergency stop switch, sensors to prevent collision, and a handheld personal computer. The rotation angle and flexion angle are measured by the ISOTRAK system and processed by computer. The wheelchair turns to the right after a head rotation to the right, and similarly for the left. A nodding movement from the operator stop the wheelchair. Operating functions can be changed by altering the computer software, so it can be easily adapted for other disabled people. The new wheelchair also features a special seating system to reinforce both the ability to control head movements and the postural stability. The subject first drove the wheelchair in a gymnasium which was wide and had a flat surface. She was able to go straight, turn right/left and stop very well. She could also propel herself a previously selected small spot. Next she drove on a pathway in an institution. By delicately controlling the direction, she could turn right/left. And an examination of her driving speed showed that an adequate speed was 2.0km/h. Moreover, we discovered that the tilt angle, which is the angle at which the chair is inclined, affected her head movement. As a result of measuring the change of position during driving, the appropriate angle found to be 22°. In the next phase, she drove on a road and sidewalk on the grounds of our rehabilitation center. She could control the direction by degrees, so that she was able to overcome the narrow width of the sidewalk and the tendency to turn downhill on a side slope. Measurement of her head movement while driving over a curb showed a shock to the neck, but it had no serious effect on control of the wheelchair. In developing a device that facilitates independence the severely disabled people, it is important to grasp the features of the individual, to make it easy to change the control functions, and to evaluate the device's actual action. The possibility of independent movement is greatly increased if all these factors are considered.