The present invention is configured to compare a signal strength based on a position value of a wireless LAN AP recorded in a wireless LAN AP position database (120) with a signal strength based on the wireless LAN AP information of nearby wireless LAN APs and a detected position value obtained through actual search performed by position detection devices (88 and 84). When the signal strength based on the wireless LAN AP information of the nearby wireless LAN APs and the detected position value obtained through actual search performed by the position detection devices (88 and 84) is higher, it means that the detected position value is closer to a corresponding wireless LAN. Accordingly, the position value of the corresponding wireless LAN AP in the wireless LAN AP position database (120) and the signal strength are updated by being replaced with the value obtained through the actual search.