The study illuminates environment_behavior study in one of the latest group living for people with dementia in Japan. The facility was designed based upon traditional Japanese residential architecture taking account of its responsiveness to the residents' lifestyle, daily activities, and rituals etc. As survey methods behavior observation and interviews with staffs were used and behavior maps of each identified residents were made every 10 minutes to record where respective residents were and what they were doing and in case of conversation whom they were talking with. The survey has been repeated three times (2, 4, and 7 months in use) on the same continuous three days of the week (Saturday, Sunday, and Monday). The results showed changes over time of the residents' spatial use patterns which suggest positive adaptive behavior. The residents' behavior is influenced by density of staff which varies among the three days.