A network display apparatus, which is connected to a network and has a thin client function, is used as a monitor of a host device. If audio and video data is received through the network while the network display apparatus is used as a monitor of the host device, the network display apparatus may transmit the audio and video data to the host device. The host device performs signal processing for the audio and video data received through the network from the network display apparatus, and outputs the processed data. Accordingly, the audio and video data received from an external apparatus through the network by the network display apparatus is output by the host device, and thus it is possible to perform operations using the host device and simultaneously to provide a user of the audio and video data received from the external apparatus without source change.