Abstract: A position detection server corrects for the attenuation of the intensity of an electric wave from each AP unit which is caused by walls by using map information to determine a distance between each AP unit and a terminal, acquires, as an existence region, a region of the position of the terminal in which variations are permitted to occur in the electric wave intensity due to the characteristics of the electric wave from the distance, restricts this existence region to an actionable region according to the state of the terminal, excludes any part which is blocked by walls when viewed from the immediately preceding position of the terminal from the actionable region by using the map information to determine a movable region, and narrows this movable region down to a region extending in the direction in which the terminal is moving to determine the position of the terminal.