An antenna made by winding a coil on the periphery of a rod-like core made
of a magnetic material is housed inside a pillar having a relatively
small width and disposed in a manner such that its axis line is nearly
orthogonal to the vertical axis line of the pillar. With this
arrangement, a predetermined communication range is secured as the
electromagnetic waves radiated from the antenna are barely absorbed by
the vehicle body and radiated to inside the cabin as well as to the
outside. Accordingly, an inexpensive antenna device and a communications
system using it are provided which enable communication with a portable
device inside and outside a vehicle cabin using a single antenna.