There is a report of depending on the mistake that it relates to drowsiness at industry and the malpractice area in the advanced country. It is important to clarify the sleep state adequately. However, there is one night stay necessity in the inspection, and the sleep polysomnography that is the inspection of the sleep specialty is not easily enforceable in the infant and the working person. Recently, the technique named videosomnography was proposed to measure the sleep state in the unrestraint and non-contact way. This is a technique for manually writing the sleeping patient’s body movement from the recorded video and evaluating the sleep at night. However, there is a problem of taking time for processing more than ten hours. In this research, we proposed the technique for automatically detecting body movement by difference image processing. To verify the validity of the proposal technique, we compared body movement measured by difference image processing and the acceleration data about subject. As a result, it was suggested that the proposal technique showed body movement future well.