To ensure isolation among a plurality of antennas, when the antennas are arrayed.

A radio wave radiator incluldes a first circuit 1 for radiating radio waves of an antenna, a filter, a balun and the like; a second circuit 2 of which the characteristics are affected by radio waves from the first circuit; and a third circuit 3, which is disposed between the first circuit and the second circuit and reduces the influences upon the second circuit caused by the radio waves of the first circuit. The third circuit includes interdigital lines 3-1 to 3-4, each including a second line 5 and a first line 4 wider than the second line one by one or more and being formed by connecting the first line and the second line in series. One end of each of the interdigital lines is grounded, and its other end is opened or short-circuited.