The symptoms of restricted joint mobility can present considerable challenges and adversely impact an individual's quality of life. Physical therapy rehabilitation is a commonly employed intervention to alleviate this issue. In this study, a passive motion device specifically designed for forearm supination and pronation was developed. The paper describes the structural analysis, design, fabrication, and evaluation of the apparatus. The device was constructed utilizing a pneumatic soft actuator that applies direct pressure to the affected region. The actuator comprises an aluminum laminated film and an air supply tube. The mechanism functions by exerting direct pressure on the wrist and executing actions on the forearm. The structure and the soft actuator underwent preliminary examination, and its design and fabrication were predicated on the study's findings. A force evaluation trial was performed, and a questionnaire was disseminated to ten participants to evaluate the device's efficacy. The outcomes demonstrated that the participants were capable of executing passive movements of internal and external rotation, and the apparatus facilitated other movements within 60% to 80% of the reference range of motion.