A mobile terminal including a source and an authentication device, wherein the authentication device is an IC card and wherein the source and the authentication device perform transmission and reception of messages with respect to each other, wherein the source comprising: an identifier generation means for generating an identifier of the source using both terminal group identification information and counter information of the authentication device prior to a request for a message to the authentication device, the counter information including a counter value uniquely generated by the authentication device and provided to the source such that the source has obtained a counter value from the authentication device that is different than a counter value that any other sources in the mobile terminal have obtained from the authentication device and the terminal group identification information identifying a group of adjoining mobile terminals including the mobile terminal; a message generation means for generating a message a source of which is defined in the message by the source identifier generated by the identifier generation means and a destination of which is defined in the message by an identifier of the authentication device; and a transmission means for transmitting the generated message to the authentication device when the identifier of the authentication device is held in a hold means, and wherein the authentication device comprising: an authentication means for judging, as to the source identifier of the message transmitted by the transmission means, whether or not the terminal group identification information and the counter information agree with the terminal group identification information and the counter information of the authentication device; and a process execution means for executing a process in accordance with the message when the authentication means judges that they agree. an identifier generation means for generating an identifier of the source using both terminal group identification information and counter information of the authentication device prior to a request for a message to the authentication device, the counter information including a counter value uniquely generated by the authentication device and provided to the source such that the source has obtained a counter value from the authentication device that is different than a counter value that any other sources in the mobile terminal have obtained from the authentication device and the terminal group identification information identifying a group of adjoining mobile terminals including the mobile terminal; a message generation means for generating a message a source of which is defined in the message by the source identifier generated by the identifier generation means and a destination of which is defined in the message by an identifier of the authentication device; and a transmission means for transmitting the generated message to the authentication device when the identifier of the authentication device is held in a hold means, and wherein the authentication device comprising: an authentication means for judging, as to the source identifier of the message transmitted by the transmission means, whether or not the terminal group identification information and the counter information agree with the terminal group identification information and the counter information of the authentication device; and a process execution means for executing a process in accordance with the message when the authentication means judges that they agree. an authentication means for judging, as to the source identifier of the message transmitted by the transmission means, whether or not the terminal group identification information and the counter information agree with the terminal group identification information and the counter information of the authentication device; and a process execution means for executing a process in accordance with the message when the authentication means judges that they agree.