A correlation matrix calculating unit calculates an unnecessary signal correlation matrix. A diagonal load processing unit performs diagonal load processing on the unnecessary signal correlation matrix. A window function calculating unit calculates a window function for obtaining a side lobe characteristic that reduces unnecessary signals on the basis of an unnecessary signal correlation matrix R after the diagonal load processing. A window function applying unit applies the window function to a reception signal vector. A beam forming unit forms a MIMO beam on the basis of the reception signal vector to which the window function is applied and a beam directivity angle.