A two-way mirroring system for sound data comprises a display device configured to output data including video or sound through a display; and a source device configured to be connected with the display device and output the data to the display device. The display device includes an audio transmission server which encodes the sound received from a sound input device receiving the sound and transmits it to the source device, and the source device includes an audio transmission client which receives the encoded sound transmitted from the audio transmission server and transmits the received, encoded sound to an application provided in its inside.