Antenna device for vehicles and vehicle antenna system and communication system using the antenna device

An antenna device (35) for installation on vehicles, which antenna device including a core (21) made of a magnetic material, a holding portion (22) provided by a dielectric film sheet wound around the core, a coil (23) formed with a linear conductor wound around the holding portion, a case (24) made of a dielectric resin material for housing the core, the holding portion and the coil, and a flexible dielectric resin (32) filling the space within the case excluding the core, the holding portion and the coil.