Abstract: A method for estimating an arrival direction of an electromagnetic wave by the BS-MUSIC, by inputting into one receiver arrival wave reception signals received by a plurality of antenna elements constituting an array antenna. At first, a wide range is scanned in a plurality of directions with a wide antenna beam and a first estimation of arrival direction is carried out. Next, a plurality of directions are scanned with a narrow antenna beam to cover only the directions obtained as a result of the first estimation of arrival direction. Thus, a second estimation of arrival direction is carried out. With this arrangement, it is possible to provide a method of estimating an arrival direction by using a small number of receivers in a small apparatus at low cost. Further, based on this method, it is also possible to estimate an arrival direction in a small calculation volume even under the unknown environment of waves.