Abstract: In order to determine the direction of a beam antenna, at least one magnetic detection device is attached to the beam antenna for measuring at least one of the horizontal and vertical components of the geomagnetic field. Maximum and minimum geomagnetic field data values are obtained from the magnetic detection devices while rotating the beam antenna. Based on output data from the at least one magnetic detection means, one or two possible direction candidates are determined. When the output data has only one possible direction candidate it is either a maximum or minimum value. The direction of the beam antenna is determined from the two direction candidates by specifying one of the candidates depending upon whether a direction of the beam antenna is to the right or left, and determining the direction of the beam antenna from one direction candidate when the output data from the at least one magnetic detection devices corresponds to the minimum or maximum geomagnetic field data.