A radar device comprising: N transmission signal generating units (3-1 to 3-N) for generating transmission signals different from each other, wherein N indicates two or more; N transmission antennas (2-1 to 2-N) for transmitting a transmission signal by being connected to the N transmission signal generating units one by one; M reception antennas (4-1 to 4-M) for receiving reflection waves of the transmission signals transmitted from the N transmission antennas, the reflection waves being formed by reflection off an object, wherein M indicates two or more; M matched filter banks (5-1 to 5-M) for each outputting a reception signal vector that is an output of a matched filter using a transmission signal generated by each of the N transmission signal generating units as a replica of the matched filter by being connected to the M reception antennas one by one; a correlation matrix calculating unit for calculating an direct propagation clutters and multipath clutters correlation matrix Rc using a steering vector of an unnecessary reflection signal defined on a basis of a transmission angle of the unnecessary reflection signal and an arrival angle of the unnecessary reflection signal; a diagonal load processing unit for performing diagonal load processing on the direct propagation clutters and multipath clutters correlation matrix Rc calculated by the correlation matrix calculating unit by adding to the direct propagation clutters and multipath clutters correlation matrix Rc a product of a diagonal load amount ε and an unit matrix I, and calculating therewith as a direct propagation clutters and multipath clutters correlation matrix after the diagonal load processing, a diagonal load-processed direct propagation clutters and multipath clutters correlation matrix R; a window function calculating unit for calculating a window function for obtaining a side lobe characteristic that reduces unnecessary reflection signals on a basis of the diagonal load-processed direct propagation clutters and multipath clutters correlation matrix R calculated by the diagonal load processing unit; a window function applying unit for multiplying the reception signal vector output from the M matched filter banks by the window function calculated by the window function calculating unit, and outputting the reception signal vector to which the window function is applied; and a beam forming unit for forming a multiple input multiple output beam on a basis of the reception signal vector output from the window function applying unit and a beam directivity angle. N transmission signal generating units (3-1 to 3-N) for generating transmission signals different from each other, wherein N indicates two or more; N transmission antennas (2-1 to 2-N) for transmitting a transmission signal by being connected to the N transmission signal generating units one by one; M reception antennas (4-1 to 4-M) for receiving reflection waves of the transmission signals transmitted from the N transmission antennas, the reflection waves being formed by reflection off an object, wherein M indicates two or more; M matched filter banks (5-1 to 5-M) for each outputting a reception signal vector that is an output of a matched filter using a transmission signal generated by each of the N transmission signal generating units as a replica of the matched filter by being connected to the M reception antennas one by one; a correlation matrix calculating unit for calculating an direct propagation clutters and multipath clutters correlation matrix Rc using a steering vector of an unnecessary reflection signal defined on a basis of a transmission angle of the unnecessary reflection signal and an arrival angle of the unnecessary reflection signal; a diagonal load processing unit for performing diagonal load processing on the direct propagation clutters and multipath clutters correlation matrix Rc calculated by the correlation matrix calculating unit by adding to the direct propagation clutters and multipath clutters correlation matrix Rc a product of a diagonal load amount ε and an unit matrix I, and calculating therewith as a direct propagation clutters and multipath clutters correlation matrix after the diagonal load processing, a diagonal load-processed direct propagation clutters and multipath clutters correlation matrix R; a window function calculating unit for calculating a window function for obtaining a side lobe characteristic that reduces unnecessary reflection signals on a basis of the diagonal load-processed direct propagation clutters and multipath clutters correlation matrix R calculated by the diagonal load processing unit; a window function applying unit for multiplying the reception signal vector output from the M matched filter banks by the window function calculated by the window function calculating unit, and outputting the reception signal vector to which the window function is applied; and a beam forming unit for forming a multiple input multiple output beam on a basis of the reception signal vector output from the window function applying unit and a beam directivity angle.