Abstract: In a data communication apparatus provided with first and second digital interfaces respectively connectable to first and second external devices, communication (including synchronous communication and asynchronous communication) is conducted between the first external device and the first digital interface. When connection between the second digital interface and the second external device is detected, priority is given to communication with the second external device connected to the second digital interface. Preferably, the data communication apparatus causes the first external device to recognize the new connection configuration. As a result, the data communication apparatus can rapidly conduct data communication with a prescribed device without imposing a large load on the network.