To provide an antenna on an altazimuth mount which maintains a directivity accuracy by correcting a directivity error due to deformation of a frame caused by wind power and sun heat by means of a constitution having one EL angle detector and a correction algorithm.

The antenna on the altazimuth mount is provided with an EL angle difference calculating means which has the EL angle detectors at both ends of the frame supporting an EL axis and calculates an angle difference of an elevation angle detected by each EL angle detector when the EL axis is distorted by the deformation of the frame due to wind power and sun heat, an EL distortion amount correcting means which corrects an EL command value based on the calculated angle difference of the elevation angle, an AZ error calculating means which calculates an azimuth angle error based on the calculated angle difference of the elevation angle, a height of the frame and a length between both ends of the frame, and an AZ distortion amount correcting means which corrects an AZ command value based on the calculated azimuth angle error.