A controller determines whether or not the map data that includes the position information of the user device and the position information of the other party can be displayed on the screen of the display panel at a predetermined reduced scale. When the result of the determination specifies that the map that includes the position information of both parties cannot be displayed at the predetermined reduced scale, the controller 11 splits the display panel into two screens, and displays the map data that include the user device position information and the map data that include the other party position information on separate screens. When the result of the determination specifies that the map that includes the position information of both parties can be displayed, the central control device displays the single map data that include the position information of both parties on the single screen of the display panel.