In recent years, there has been a sharp increase in the number of elderly people in South Korea; this has led to rising costs and concerns on the quality of physical therapy treatment involving rehabilitation robotic devices. Therefore, the government has asked academia to expand its research scope to evaluate the usability of these devices. Hence, this study aimed to identify the major factors influencing the usability of a rehabilitation robotic device for lower limbs and the reasons for involving several diverse user groups for a more comprehensive evaluation. To measure usability as perceived by three primary user groups of user experience (UX) professionals, rehab professionals, and lay people, this study collected 196 survey. The results of an EFA showed that among three general... quality factors and five device specific factors, visual pertinence, use confidence, and safety were the critical factors influencing usability, and the results of ANOVA offered that there was discrepancy in the influential factors, namely visual pertinence, transferring, and holding the body. These findings indicate that the necessity of employing a posture-centered approach and multiple user groups in assessing the usability of rehabilitation devices. Given these findings, it is suggested that the industry and design community should move toward implementing a more explorative perspective to enable a more human-centered and posture-concerned approach to provide better usability to the diverse users of medical devices.