The prevention of falls the elderly is an important issue. It is recommended that bed exit alarms are used for warning caregivers when the elderly person with high risk of falling attempt to leave their beds. Therefore, we developed a system which assesses the posture of a person in bed from his/her shoulder and hip movement. A purpose of this study is to identify the performance of the system and the value in the care settings. In this study, the subjects were healthy adult and dementia elderly person in a nusing home. In order to evaluate the accuracy of measurement of the actual posture and its results by the system, we reviewed the recorded videos or nursing records. As a result, it was confirmed that this system is possible to determine almost exactly the different posture of the subject on the bed. Through the measuring results of the device, it was suggested that this can also be utilized as the activity log of the elderly person.