A plate member is adapted to be electrically grounded. A first radiating electrode opposes the plate member with a gap and extending parallel to the plate member. A second radiating electrode opposes the plate member with a gap and extending parallel to the plate member. A feeding pin is connected to a center part of the first radiating electrode and a center part of the second radiating electrode. The feeding pin is adapted to feed power to the first radiating electrode and the second radiating electrode. A pair of first short-circuiting pins are electrically connecting the plate member and an outer edge of the first radiating electrode at symmetrical positions relative to the feeding pin. A pair of second short-circuiting pins are electrically connecting the plate member and both ends of the second radiating electrode. The first radiating electrode is formed with blank portions which are located at such positions that are on hypothetical straight lines connecting the feeding pin and the short pins. The first radiating electrode and the second radiating electrode are flush with each other.