1. A device for detecting an azimuth viewed from the device which is present in a field, the device comprising: a transmission array antenna having a plurality of transmission antenna elements arrayed along an array axis set in advance and a receiving array antenna having a plurality of receiving antenna elements arrayed along the array axis; a signal acquiring means for acquiring a reception signal for each of channels by transmitting and receiving a search wave through each of the channels, the channels being arbitrary combinations of each of the transmission antenna elements and each of the receiving antenna elements; a first analyzing means for performing a first spatial frequency analysis along the array axis of either ones of the transmission antenna elements and the receiving antenna elements using the reception signal acquired by the signal acquiring means; a second analyzing means for performing a second spatial frequency analysis along the array axis of the other ones of the transmission antenna elements and the receiving antenna elements using results of the first spatial frequency analysis; and an azimuth calculating means for determining an azimuth of a target that has reflected the search signal in adherence to analysis results from the second spatial frequency analysis.