An antenna device to be mounted to a vehicle roof, includes: a case unit having an accommodating space formed therein and having a radio wave permeability; and an antenna unit to be accommodated in the accommodating space, wherein the antenna unit has: a pair of capacitance loading elements facing across a plane, as a center, perpendicular to the vehicle roof at a predetermined interval and at a predetermined angle to each other; a coupling portion provided at a portion lower than an upper edge of the pair of the capacitance loading elements to conduct each of the pair of capacitance loading elements each other via each of the coupling portions; and a helical element electrically connected to the coupling portions.