To provide a communication terminal which has plural modular jacks of the same shape and automatically copes with connection between modular jacks and lines to prevent the device from being left in the state that communication is impossible and doesn't require an operator to connect them again at each time.

The device is provided with a relay (connection switch means) 12, a tone detection part (line detection means) 3, and a control means 1. When the tone detection part 3 detects that an extension is connected to a first modular jack 14, the control means 1 switches the first modular jack 14 to a modular jack for extension connection to control communication; and when the tone detection part 3 detects that an outside line is connected to a second modular jack 15, the control means 1 switches the second modular jack 15 to a modular jack for outside line connection to control communication.