An antenna device includes a ground portion including a linear portion connecting a first point and a second point to each other along a first direction parallel to a surface of a substrate, on one side in a second direction orthogonal to the first direction, a power feeding portion provided in a first range including the first point, and an element portion configured to receive power from the power feeding portion and formed in a conductor portion of the substrate that is insulated from the ground portion in a state in which the element portion protrudes from the first range toward the other side in the second direction. The element portion includes a first element portion protruding in the first range toward the other side in the second direction, and a second element portion extending along the first direction from the first element portion toward the second point.