To suppress the increase of the noise resulting from an inverse filtering process of radar signals, thereby improving the resolution even for signals of a low S/N ratio.

For radar received signals a plurality of Wiener inverse filters 12-1 to 12-n are provided in parallel, and Fourier transformation coefficients αof transfer functions thereof are set to different values ranging from 0 to 1. After filtering the signals, a geometric mean processor 13 takes a geometric mean value of the filtered signals, this indicating the synergistic effect of the resolution improving effect of smaller α with that of larger α. Thus, it makes possible to raise the resolution for near-range targets at a low noise for radar received signals of low S/N ratio.