Earphone antenna and portable radio equipment provided with earphone antenna

Earphone antenna includes: earphone cable having signal lines; shield cable, and signal lines for audio signal and grounding wire, external thereof covered with shield wire, one end of shield cable connected to main body of radio equipment via multipin connector; and connection block connecting other end of shield cable to earphone cable. In connection block, audio signal transmission path is formed by connecting signal lines and grounding wire respectively to signal lines via high frequency choke exhibiting low impedance for audio signal and high impedance for high frequency signal, and connecting central conductor of coaxial cable and shield wire to unbalanced part of balun, connecting signal lines to one end of balanced part of balun via capacitor exhibiting high impedance for audio signal and low impedance for high frequency signal, and connecting other end of balanced part of balun to shield wire covering axial cable and signal lines, so that dipole antenna is formed with earphone cable and shield wire.