An antenna device includes a dielectric substrate, a ground plate arranged on a first surface of the dielectric substrate, an antenna part arranged on a second surface of the dielectric substrate, and a reflecting part. The reflecting part is arranged around the antenna part and has a plurality of conductor patches each functioning as a reflecting plate. The plurality of conductor patches form a plurality of blocks aligned along a predetermined block arrangement direction. The plurality of blocks are configured such that phases of reflected waves at an operating frequency are different for each of the blocks and phase differences of reflected waves between adjacent blocks are non-uniformly different for each of the adjacent blocks.