An antenna device includes a substrate having a base material containing a dielectric and a conductor, a waveguide, an antenna, and a matching portion arranged in the base material as a part of the conductor. The antenna faces the upper wall portion, and has a plurality of patch portions arranged in an array, a plurality of feeding lines extending in a direction from the patch portion and individually provided for the patch portions, and a plurality of short-circuit portions individually provided for the patch portions and electrically connecting the patch portion and the upper wall portion. The upper wall portion has a plurality of openings 34 individually formed with respect to the feeding lines. Each of the feeding lines extends into the waveguide through the corresponding opening.