In an antenna device including an antenna element and a feeder line to supply power to the antenna element, the antenna device includes: a front surface feeder line and a rear surface feeder line on front and rear surfaces of a substrate; opposing upper-side and lower-side ground plates across the substrate; a coaxial cable including a center conductor connected to the front surface feeder line and the rear surface feeder line and an outer conductor connected to the upper-side ground plate; and a center conductor connection fitting including a substrate connection portion inserted between the upper-side ground plate and the lower-side ground plate and a first cable connection portion protruding to outside of the upper-side ground plate. First connection pieces of the substrate connection portion are connected to the front surface feeder line, and a second connection piece is connected to the rear surface feeder line.