a first earphone cable including a pair of insulation-coated first signal lines for supplying audio signals to an earphone;

a shielded cable including a coaxial cable, an insulation-coated second signal line for audio signals and a grounding wire, the coaxial cable having a central conductor passing high frequency signals surrounded by an insulator and further surrounded by a first shield wire, the coaxial cable, the second signal line and the grounding wire collectively being surrounded by an insulation material and a second shield wire;

a multipin connector arranged on one end of the shielded cable and adapted to electrically connect the shielded cable to a radio apparatus; and

a connection block interconnecting the other end of the shielded cable and the first earphone cable, the connection block including a balun for carrying out impedance and balanced/unbalanced mode transformation, and an audio signal transmission path formed by connecting the second signal line for audio signals and the grounding wire, respectively, to the pair of first signal lines via a high frequency choke which exhibits low impedance in a frequency range of audio signals and high impedance in a frequency range of high frequency signals;

wherein connecting the central conductor of the coaxial cable and the first shield wire to an unbalanced part of the balun, connecting the pair of first signal lines to one end of a balanced part of the balun via a capacitor which exhibits high impedance in the frequency range of audio signals and low impedance in the frequency range of high frequency signals, and connecting the other end of the balanced part of the balun to the second shield wire causes formation of a dipole antenna by the first earphone cable and the second shield wire.