To maintain the angle resolution of a seeker constant even by being used in a blocking environment and to improve the target sensing capability by correcting the resolution of the seeker according to a K value and a threshold value set for every angle from a previously measured beam pattern.

Video signals 1aΣ, 1bΔ are integrated by an integral processor 2, a CFAR processor 3 removes clutters, and input to a Σ-K*Δ processor 11. Here, a K value setter 14 reads a K value corresponding to a beam directing angle θ from a K value set at every beam pattern angle already measured by a K value table 13, and the processor 11 processes the input signal according to the K value. A binarization decision processor 15, which inputs a target reflecting echo after processing, binarization decides whether the echo exceeds the threshold value or not from a threshold setter 17, and outputs a target detection signal 18 by clearing it. In this case, the setter 17 reads the threshold value corresponding to the angle θ from the threshold value set and stored by a threshold table 16 similarly to the table 13, and outputs the threshold value.