Recently, the number of bedridden patients has increased because of the rapid growth in the aging population worldwide, and most of them have lived on an electric adjustable bed (EAB). Caring for these patients on an EAB is easier and more comfortable than on the floor or a manual adjustable bed. However, the use of an EAB has a negative effect on the slip length and the dorsal and abdomen loads on the patients. Therefore, the aim of this research was to evaluate the usability elements by elevation of the EAB's back support using a motion analysis. In this study, an experiment with 10 subjects (5 men, 5 women, 29.9 ± 2.28 years, 165.8 ± 8.26 cm, 64.2 ± 11.7 kg; mean ± SD) was carried out. The relative motions of the EAB and subjects were captured by a motion analysis system using a customized marker set (EAB: 24 markers, subject: 16 markers, U.E.T.C.). The results of this study show that the slip length and the dorsal and abdomen loads increased as the back support of the EAB was further elevated, and the slip length and dorsal load were not restored when the elevation angle was returned to 0°.A trend toward decrease in changing rate of dorsal load while increase of abdomen load were observed when the back support was elevated from Sections II-1 and II-2 (head-of-bed elevation from 30° to 60°). It would be expected that development of new care technology and care service would be possible with the results and methods of this study.