In accordance with one of embodiments of the present invention, a frequency resolution processing unit calculates complex number data based on a beat signal caused by a receiving wave coming from a target and a transmission wave. A target detection unit detects a peak value from the intensities of beat frequencies, and then detects an existence of the target. The target link unit makes association between a target detected in the present detecting cycle and the target detected in the past detecting cycle. A direction estimating unit generates a generative complex number data based on the complex number data so as to correspond to a data generation unit. The direction estimating unit calculates, for each antenna, an incoming direction of the receiving wave based on each of normal equations formed by use of the complex number data of the beat frequency which an existence of the target is detected and the generative complex number data.