Disclosed herein is an antenna system comprising a plurality of element antennas, a plurality of variable phase shifters and a plurality of variable amplitude type devices connected to the plurality of element antennas respectively, and an arithmetic unit used to perform the arithmetical operation of the excitation amplitude and phase for exciting each of the plurality of element antennas. The arithmetic unit includes the four means and performs the arithmetical operation of the excitation amplitude and phase used to define a desired radiation pattern composed by each of the element antennas with respect to a preset allowable variation width D of the excitation amplitude. Since the arithmetic unit serves to fix the excitation amplitude and perform the arithmetical operation of the excitation phase separately, the antenna system capable of performing the arithmetical operation of the excitation amplitude and phase for obtaining a desired radiation pattern with respect to the preset allowable variation width D of the excitation amplitude, and obtaining a desired radiation pattern even when the allowable variation width D of the excitation amplitude is given, can be realized.