The objective of the present invention is to provide a connection cable
that serves as an external antenna for a radio apparatus, and whose
antenna performance is not deteriorated in the use state by an adverse
affect attributable to the near proximity of a human body.According to
the present invention, an antenna device, integrally formed with first
connection means, which is to be connected to a radio apparatus, second
connection means, which is to be connected to a peripheral device, and a
connection cable and an antenna element, which are located in between and
which transmit a plurality of signals from the radio apparatus to the
peripheral device, includes: first relay means, located at a middle
position in the connection cable, for relaying the plurality of signals;
the antenna element, located between the second connection means and the
first relay means; and a coaxial line, located between the first
connection means and the first relay means for transmitting, to the radio
apparatus, an antenna reception signal that has been received at the
antenna element and has been extracted by the first relay means, wherein
the antenna element serves as an external antenna for the radio
apparatus.