A system control circuit 5 determines whether or not an external apparatus connected to an interface 14 is one that can store data, by transmitting data to the apparatus through the interface 14. It the system control circuit 5 determines that the external apparatus can store data, the circuit 5 turns off a switch 13, stopping the transmission of audio data to the external apparatus through the interface 14. As a result, illegal copying of the data can be effectively prevented.