A computer system is provided with an antenna which disables inappropriate wireless communications when a communication controller is inconsistently connected with the antenna. The computer having a diversity antenna connected to a detachable wireless LAN card containing a controller for providing wireless communication is mounted in a mini PCI slot, comprising a switch device for recognizing the identification information (ID) of the wireless LAN card to be mounted by BIOS executed on a CPU, in which the connection between the diversity antenna and the wireless LAN card is maintained in an off state (default) as an initial state in which the wireless LAN card is mounted, and the connection is enabled based on the identification information recognized by the BIOS.