PURPOSE: To obtain an antenna system radiating a radio wave without power loss even when an object comes in the vicinity of antenna elements by adopting the constitution such that power is supplied from one terminal of a circulator and two remaining terminals connect to a 1st antenna system and a 2nd antenna system respectively.

CONSTITUTION: In the case of a free space, feeding power is fed only to a 1st antenna element by a circular 11 and a radiation pattern 12 of the antenna element comes from only the 1st antenna element. When an object 9 exists near the antenna element 11, the impedance of the element 1 is changed and reflection is caused. Thus, the power from the feeding point enters once the element 1 and does not return to the feeding point by the circulator 11 and is fed to a 2nd antenna element 2. Thus, a radio wave radiates from the element 2 and no power loss is caused. When an object exists in the vicinity of the 2nd antenna element 2, the vicinity of the element 2 is not energized; the radiation characteristic is unchanged and no power loss is caused.