A communication system is provided in which multiple terminal devices form a group and at least one base station device assigns a channel to each group, so that communication from a terminal device included in a group assigned a channel to the other terminal devices included in the group is performed. In the communication system, a transmitting unit transmits information about authentication to a base station device before communication is started. A receiving unit receives, from a base station device, information about authentication status of at least another terminal device within the group.