An antenna device has a plane ground conductor plate, and two radiating conductors disposed on the upper side of the plane ground conductor plate in parallel to and adjacently to each other so as to be symmetrical with each other with reference to the center of the plane ground plate. The radiating plates are individually provided with respective feeder ports, and are operated independently from each other. End portions of the radiating conductors may be bent to be substantially perpendicular to the plane ground plate in a direction of achieving a maximum gain, whereby isolation between the feeder ports can be enhanced. With this antenna device, antenna directivity can be secured, a high antenna gain can be obtained, and the going-round of a current from a transmitting unit to a receiving unit can be suppressed favorably.