Recently, robot-assisted joint replacement surgeries are on the rise. Robot-assisted surgery can make more accurate outcome, and thus it will be more popular. For the accurate result, secure fixation of bone is necessary, but there are numerous difficulties for the secure fixation. Detecting bone motion is necessary to prevent some errors. Currently, optical sensor and location sensor are in use; however, these sensors can cause interventional problem for the friction between mechanical devices. This study shows how to compose the bone motion detecting device using electromagnetic sensor, how to commercialize the bone motion detecting device.