An earphone apparatus is designed for an audio device and a portable communication terminal device. The earphone apparatus includes a first plug for disconnectable connection with the audio device, and a second plug for disconnectable connection with the portable communication terminal device. An electroacoustical transducer connected to the first plug and the second plug is operative for converting a first electric signal transmitted via the first plug into corresponding sound, and for converting a second electric signal transmitted via the second plug into corresponding sound. A suitable controller provided between the first plug and the electroacoustical transducer is operative for controlling a level of the first electric signal transmitted to the electroacoustical transducer.