The electric wheelchair controlled with a joystick has become an important form of transportation for severely disabled-people. The wheelchair can be operated easily at any speed and in any direction by tilting the joystick to certain angles and directions. But some accidents involving the joystick-type electric wheelchair may occur as, for example, unintended movements of the joystick are caused through involuntary movements by users with disabilities. Accordingly, some differences are found between how the joystick is operated and how the joystick actually moves; thus training is required for beginners among joystick users. Difficulty in using the joystick causes operational errors because the user feels stress caused by its operation while controlling the wheelchair. These types of accidents have been occurring intermittently. Aiming to solve such problems, research and development of an automatic-driving device has been conducted in order to secure safety in driving electric wheelchairs. But so far research has not been conducted into developing an operation-assist device. This type of device can be loaded onto an existing electric wheelchair as an additional device in order to prevent driving accidents, while keeping the additional cost very low. The device in this study was developed and was loaded onto an existing electric wheelchair so that the safety of users of existing electric wheelchairs can be easily assured while at the same time the cost is kept low. The number of electric wheelchairs has already amounted to about 100,000 in Japan. To achieve the aim, a method of measuring a distance by using ultrasonic waves is applied in order to develop a device which can automatically prevent the electric wheelchair from crashing into walls on the left and right sides of the wheelchair. Movements of the wheelchair in forward and back directions are controlled according to the driver's intention. Experiments conducted by using an electric wheelchair loaded with the newly designed device have verified that the wheelchair can drive safely while automatically detecting walls on the left and right sides of the wheelchair and other obstacles.