Display devices are connected with a content server mounted inside a vehicle by a wireless communication technology as stipulated in IEEE802.11b. The content server and display devices share common keys (encryption key and corresponding decryption key) acted on by key creation information consisting of information about the vehicle. The content server reads out stored contents according to requests from the display devices. The read contents are then encrypted using the encryption key shared with the display devices and sent to the display devices. The invention can be applied to a wireless communication system consisting of devices which communicate data by wireless communication technology within the vehicle.