Abstract: There is disclosed a method for controlling the position of a mobile host in a local area network (LAN), whereby the movement of the mobile host out of a certain LAN can be quickly detected even when the mobile host transmits no frames and invalid traffic can be reduced. A server 3 duplicates a learning function table in a bridge device 2 at each specified time. Location confirmation is performed for the currently connected mobile host based on this duplicated information at each specified time. If the mobile host gives no response to the location confirmation, the movement of this mobile host is determined and the learning function table in the bridge device 2 is renewed. Thus, even when the mobile host is moved out of the LAN and no frames are transmitted therefrom, the movement of the mobile host can be quickly detected and invalid traffic can be reduced.