Circadian rhythms (CRs) of human have a role to maintain our mind and body together with our health. Thus, a disorder of CRs is a serious problem because it evokes critical disease. In this society, we have a lot of factor that causes a disorder of CRs, such as a social stress and a light of smartphone in the night. Hence, observing our CRs ourselves is an efficient method to prevent it. We are supposed to realize it with a simple electroencephalographic (EEG) device which allows us to measure an EEG signal easily in our daily life. In this research, we investigate the possibility of detecting CRs by a simple EEG device. Sleeping is one of the functions of CRs but it would be thrown into disorder by watching smartphone at the night. Thus, we examine the time required to falling asleep as a behavior of CRs which could be influenced by watching smartphone. Our goal is to detect and identify the CRs of 24 hours by a simple EEG device.