In a planar antenna, a plate member is adapted to be electrically grounded. A radiating electrode is opposing the plate member with a gap and extending parallel to the plate member. A feeding pin is disposed at a center part of the radiating electrode, and adapted to feed power to the radiating electrode. At least one pair of short pins is electrically connecting the plate member and an outer edge of the radiating electrode at symmetrical positions relative to the feeding pin. The 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.