An antenna mirror surface measuring/adjusting apparatus has a plane mirror larger than an aperture surface of said principal reflection mirror and set in parallel with the aperture surface, an actuator for driving a group of mirror surface panels of the principal reflection mirror, and a receiving electric field arithmetic processor for measuring, each time the actuator shifts a position of the mirror surface panel from an initial state of the mirror surface panel of the principal reflection mirror, radio wave signals of radio waves radiated by a transmitter/receiver and reflected back from the plane mirror, obtaining an aperture surface phase distribution in an initial state of the principal reflection mirror by executing an arithmetic process on these measured signals, then gaining configurations of the mirror surface on the basis of the aperture surface phase distribution, and adjusting the mirror surface by the actuator in accordance with the obtained mirror surface configurations. Accordingly, a measurement frequency is freely selected, and the measurement can be carried out in an ideal measurement environment of not being influenced by changes in wind, sunlight and temperature, whereby the mirror surface can be adjusted with high accuracy.