Disclosed herein is an antenna device that includes: a metal layer having a first metal plate, a second metal plate that is adjacent to the first metal plate across a slit extending in a first direction, and a connecting part extends over the slit to connect the first metal plate to the second metal plate such that the first and second metal plate are integrated; and an antenna coil having an antenna axis substantially perpendicular to a main surface of the metal layer and defining an inner diameter area surrounded by an innermost line thereof. The inner diameter area of the antenna coil overlaps with the slit in planar view. The slit has a narrower width than the inner diameter area of the antenna coil. The antenna coil has a first exposed part and a second exposed part intersecting with the slit.