PURPOSE: To provide sure beam directivity control and to prolong the service life of a satellite by controlling the directional point of an antenna beam by calculating the fluctuating amount of a beam directing point based on the inclination angle of a track surface, eccentricity and up cross-section time.

CONSTITUTION: Concerning an antenna 10, the fluctuation of the beam directing point with the daily movement is calculated by a directivity control means based on the track surface inclination angle, eccentricity and up cross-section time of a triaxial posture control satellute stored in a RAM 15, and the direction of beam directivity is controlled so as to cancel the fluctuation. Thus, the beam directing point of the antenna can be controlled without the south-north track control of the triaxial posture control satellite itself, mounted fuel can be reduced by reducing the frequency of using a thruster for posture control and as a result, the service life of the satellite is prolonged. Further, since very complicated thruster jetting operations are reduced for satellite control, the safety as a satellite system is improved.