An antenna (10, 20, 30, 40, 50, 60, 80) comprising: (a) a first conductor layer comprising a first opening part surrounded by a first split ring part, the first split ring part being continuous in an approximate C-shape, the open ends of the C-shaped first split ring part being separated by a first slot-shaped split part and connecting the first opening part with an edge of the first conductor layer; (b) a second conductor layer (7B, 7C) comprising a second opening part surrounded by a second split ring part (2, 21), the second split ring part being continuous in an approximate C-shape, the open ends of the C-shaped second split ring part being separated by a second slot-shaped split part (6b, 6c) and connecting the second opening part with an edge of the second conductor layer, the second split ring part overlapping the first split ring part, the second conductor layer being parallel to the first conductor layer; (c) a plurality of conductor vias provided with an interval in a circumferential direction of the first split ring part and the second split ring part, the conductor vias electrically connecting the first split ring part and the second split ring part; and (d) a power feed line provided on a conductor layer (7B, 7C) different from the first conductor layer, the power feed line having a first end and a second end, the first end being electrically connected to at least one of the conductor vias, the second end extending to a region of the conductor layer different from the first conductor layer opposing the edge of the first conductor layer, (e) the first split part is shorter than a short side or diameter of the first opening part, and the second split part is shorter than a short side or diameter of the second opening part, characterized in that (f) the power feed line extends in a straight line from the first end to the second end in a direction away from and perpendicular to the edge of the first conductor layer and the power feed line spans the first and the second opening parts. (a) a first conductor layer comprising a first opening part surrounded by a first split ring part, the first split ring part being continuous in an approximate C-shape, the open ends of the C-shaped first split ring part being separated by a first slot-shaped split part and connecting the first opening part with an edge of the first conductor layer; (b) a second conductor layer (7B, 7C) comprising a second opening part surrounded by a second split ring part (2, 21), the second split ring part being continuous in an approximate C-shape, the open ends of the C-shaped second split ring part being separated by a second slot-shaped split part (6b, 6c) and connecting the second opening part with an edge of the second conductor layer, the second split ring part overlapping the first split ring part, the second conductor layer being parallel to the first conductor layer; (c) a plurality of conductor vias provided with an interval in a circumferential direction of the first split ring part and the second split ring part, the conductor vias electrically connecting the first split ring part and the second split ring part; and (d) a power feed line provided on a conductor layer (7B, 7C) different from the first conductor layer, the power feed line having a first end and a second end, the first end being electrically connected to at least one of the conductor vias, the second end extending to a region of the conductor layer different from the first conductor layer opposing the edge of the first conductor layer, (e) the first split part is shorter than a short side or diameter of the first opening part, and the second split part is shorter than a short side or diameter of the second opening part, characterized in that (f) the power feed line extends in a straight line from the first end to the second end in a direction away from and perpendicular to the edge of the first conductor layer and the power feed line spans the first and the second opening parts.