The safety of physically disabled persons must be considered during the initial developmental stages of a rehabilitative or assistive device to prevent death or injury. Thus, in the research field of biomedical engineering, researchers specializing in physical assistive system development must take the initiative to ensure user safety. This paper proposes methods to plan and implement safety measures for physical assistive systems, using a wheelchair-compatible system with sit-to-stand (STS) movement support as an example. To promote daily independent active exercise and motor learning with progressively less assistance from specialists, the support system does not require the attachment of any device or sensor onto the user’s body. To ensure safety, we first identified the possible dangers of injury or other potential hazards involved in STS movement support. Next, we developed safety measures to prevent all the identified dangers of injury and hazards. The steps taken to develop these safety measures were submitted for ethical review. Finally, we confirmed the effectiveness of the safety measures developed by conducting fundamental and realistic experiments. The safety measures described in this paper were developed for the STS support system, but the method used to identify the required safety measures can be implemented in the development of any physical assistive system. The proposed method will help engineers to improve the safety of rehabilitative and assistive devices.