a reliability extracting section extracts the reliability of positioning at a person &# 39 ; s position calculator on the basis of an image captured from an imaging section . a section that creates a possibly - existing area determines a possibly - existing area on the basis of the result of positioning obtained by the person &# 39 ; s position calculator and reliability obtained by the reliability extracting section . an entry determining section determines entering and / or leaving to / from a targeted monitored area on the basis of the overlapping of the possibly - existing area with the monitored area .