A low-profile antenna device is provided for a vehicle. The low-profile antenna device includes a base plate, a circuit board, a base, a top-load element and a coil. The circuit board is disposed on the base plate, in parallel with the base plate. An amplifier circuit is placed on a front surface side of the circuit board, and a ground plate area having a ground plate and an empty area not having a ground plate are provided on a back, surface of the circuit board. The coil is disposed on the front surface side of the circuit board facing the empty area of the circuit board. The coil is disposed in a manner axially parallel with the circuit board, connected between the top-load element and the amplifier circuit, and adjusted to function as a resonance antenna.