To achieve the required angle measuring accuracy by increasing arm length even if the frequency of a geostationary satellite is low, i.e., without increasing the bore of an antenna.

First and second mobile reflectors 2a, 2b are installed at both ends of an arm 1 which makes rotational movement and first and second fixed reflectors 4a, 4b are installed on the ground. The reflecting directions of the first and second mobile reflectors 2a, 2b and the first and second fixed reflectors 4a, 4b are varied so that first and second antennas 5a, 5b installed on the ground always receive the electric waves of a geostationary satellite S even with the rotation of the arm 1. The electric wave signals received by the antennas 5a, 5b are subjected to correlation process to determine the time difference T' required for the signals emitted by the geostationary satellite S to arrive at the antennas 5a, 5b and the time difference T' is corrected to obtain a corrected time difference T. On the basis of a curve in the form of a sinusoidal wave described by the measurements of the time difference as the rotational angle of the arm 1 varies from 0 to 360 degrees, its amplitude and phase are read to determine the elevation angle and the azimuth of the geostationary satellite S.