An antenna device is provided. The antenna includes a feeding end, a grounding end, a loop metal portion and a protruded metal portion. The grounding end is electrically connected to a ground plane. The loop metal portion extends from the feeding end to the grounding end to form a loop antenna structure. The protruded metal portion is electrically connected to the loop metal portion, wherein the distance between the protruded metal portion and the grounding end is shorter than the distance between the protruded metal portion and the feeding end.