Electric Wheelchair (hereinafter “EWC”) is one of the welfare tools (technical aide) that have been most widely used for person of the physically disability and the elderly person to do the social life smoothly, but if the person of the physically disability, etc. want to lead comfortable and safe life with EWC, they are requested to have the “ability to run EWC safely.” However, it is not necessarily clear what the operation “ability to run EWC safely” is, or how this can be understood. Then in this study, mainly targeting for the users of EWC run by the joystick manipulation, we tried to estimate the ability to operate EWC safely by means of using the “computerized intelligence test” and the program to understand the “response time to the speed.” As a result, the regular users of EWC showed an equal or more advanced mental work ability and response time to the speed compared to those of person of the mentally disorder whose intelligence age is estimated to be around 10-12 years old, and non-EWC users could not reach this level. We think that with this mental work ability and the response to the speed as the indices, the decision on wrong/right of the EWC use would become possible by estimating if a user has an ability to run EWC steadily or not.