To provide an omnidirectional antenna which freely selects a polarization mode with high gain and is widely used as components of broadcasting, relay, communication, traffic control and traveling object communication, and whose set frequency band is suitable to be widely used for an HF, a VHF and a UHF.

In this rectangular frame type plane radiation element, the ratio of a short side and a long side 1 is 1:4 to 8, the length of the side 1 is equal to one wavelength of a center frequency of a used electric wave, and short bars 3 are arranged on a pair of long sides 1 at 1/4 to 1/40 distance of the entire length of the side 1 from both edge planes. One wavelength type plane radiation element N is configured as a type which has conductive paths 4 for feeding which are symmetrically bent outside respective frames at a central part of the long sides with parts of 1/10 to 1/30 distance of the long sides at the angle of 45°C and feeds from the positions 5 outside the frame which are slightly separated from the center position of both long sides 1.