To obtain an array antenna system of a mono-pulse system, which has a very small loss with a simple configuration.

The array antenna 6 energized by a radial line 1 is provided with a sum signal feeder probe 7 that is placed nearly at a center point of the radial line 1, two respective difference signal feeder probes 8a, 8b and 9a, 9b at nearly symmetrical positions with respect to a center point of the radian line on a horizontal plane axis of the radial line formed to each of desired cut-faces of the array antenna 6, a sum signal transmission line 10 connected to the sum signal feeder probe 7, and difference signal forming circuits 11a, 11b connected to the difference signal feeder probes 8a, 8b and 9a, 9b.