An adapter is provided for a communication device. The adapter includes an elongated hollow shell and a foldable adapting element. The foldable adapting element includes an input half part and an output half part pivotally rotatable with each other between an expansion accommodating position and a fold operation position. The output half part includes an output port for a transmission connector in the communication device. The input half part includes a set of power input ends corresponding to the power output port in the back cover mobile power source of the communication device. When located in the fold operation position, the output port can be plugged into the transmission connector, and the power input ends can be correspondingly connected to the power output port.