A wireless LAN device for lessening failure in switching from infrastructure mode to ad-hoc mode. A radio wave coverage storage stores coverage information about coverage of radio waves amongst access points. A terminal information storage stores terminal information about terminals associated with the access points. A packet receiver receives, via the access points, a packet transmitted from any of the terminals in infrastructure mode. An access point acquisition unit looks up the terminal information storage, based on terminal information about originating and destination terminals contained in the packet, to identify access points with which the terminals are associated. A radio wave coverage decision unit looks up the radio wave coverage storage to determine whether the identified access points are within each other's coverage of radio waves. A communication mode switch switches the communication mode of the originating and destination terminals to ad-hoc mode in accordance with the determination result.