A terminal main body of a communication terminal is supplied power from a battery pack through a DC signal path. The terminal main body communicates with at least one additional function module providing an additional function through a communication path connected to the DC signal path so as to provide the additional function to a user. Herein, the communication path is an AC signal path. That is, a signal transmitted/received between the terminal main body and the additional function module is an AC signal, and thus, the communication path can be compatible with the DC signal path providing the power. In addition, a plurality of additional function modules can be serially connected in the form of a serial communication bus, and therefore, a user can select a plurality of additional functions.