A sampled beat signal RD is split into a plurality of short-time data SD in the time direction, for each of antenna elements. Interference component frequency of an interference wave is detected from a frequency spectrum of the short-time data SD. A digital beam forming process is performed for the interference component frequency of the interference wave to extract a peak of the electrical power of an azimuth direction and estimate an absolute value of an incoming direction of interference components. Based on the absolute value of the incoming direction of the estimated interference components, a filter for suppressing the interference components is operated to suppress the interference components.