A signal processing device comprising: - a signal combining means (1; 11) configured to, when reception antennas, which are disposed along an orbital direction of a platform in which a radar device is mounted, receive signals which are included in signals repeatedly transmitted from a transmitting antenna and which are reflected by a stationary target and a moving target, combine the received signals of the reception antennas in such a way that aliasing noise components associated with the stationary target and included in the received signals of the reception antennas are canceled out, thereby to output a composite signal; - a moving target component extracting means (3, 4) configured to suppress a stationary target component and an aliasing noise component associated with the moving target, the stationary target component and the aliasing noise component being included in the composite signal output from the signal combining means (1; 11), and extract a moving target component included in the composite signal; and - an image reconstructing means (2, 5) configured to reconstruct an image of the moving target from the moving target component extracted by the moving target component extracting means (3, 4), wherein the signal combining means (1; 11) comprises: - a signal converter (1a; 11a) configured to convert the received signals of the reception antennas into signals in a frequency domain; and - a signal combiner (ab; 11b) configured to cyclically shift the signals in the frequency domain by one-half of a pulse repetition frequency of the signals transmitted from the transmitting antenna thereby to generate shifted signals, and combine the shifted signals in the frequency domain to thereby cause aliasing noise components associated with the stationary target and included in the signals in the frequency domain to be canceled out, thereby to output the composite signal, wherein the moving target component extracting means (3, 4) comprises: - a rearrangement unit configured to make a copy of a signal in the composite signal and perform replacement thereby to rearrange a spectrum of the composite signal in such a way that the stationary target component and the aliasing noise component associated with the moving target, included in the composite signal, and the moving target component included in the composite signal are separate on the frequency domain; and - a formation unit configured to suppress the stationary target component and the aliasing noise component associated with the moving target, included in the composite signal whose spectrum is rearranged by the rearrangement unit, and extract the moving target component included in the composite signal whose spectrum is rearranged by the rearrangement unit. - a signal combining means (1; 11) configured to, when reception antennas, which are disposed along an orbital direction of a platform in which a radar device is mounted, receive signals which are included in signals repeatedly transmitted from a transmitting antenna and which are reflected by a stationary target and a moving target, combine the received signals of the reception antennas in such a way that aliasing noise components associated with the stationary target and included in the received signals of the reception antennas are canceled out, thereby to output a composite signal; - a moving target component extracting means (3, 4) configured to suppress a stationary target component and an aliasing noise component associated with the moving target, the stationary target component and the aliasing noise component being included in the composite signal output from the signal combining means (1; 11), and extract a moving target component included in the composite signal; and - an image reconstructing means (2, 5) configured to reconstruct an image of the moving target from the moving target component extracted by the moving target component extracting means (3, 4), - a signal converter (1a; 11a) configured to convert the received signals of the reception antennas into signals in a frequency domain; and - a signal combiner (ab; 11b) configured to cyclically shift the signals in the frequency domain by one-half of a pulse repetition frequency of the signals transmitted from the transmitting antenna thereby to generate shifted signals, and combine the shifted signals in the frequency domain to thereby cause aliasing noise components associated with the stationary target and included in the signals in the frequency domain to be canceled out, thereby to output the composite signal, - a rearrangement unit configured to make a copy of a signal in the composite signal and perform replacement thereby to rearrange a spectrum of the composite signal in such a way that the stationary target component and the aliasing noise component associated with the moving target, included in the composite signal, and the moving target component included in the composite signal are separate on the frequency domain; and - a formation unit configured to suppress the stationary target component and the aliasing noise component associated with the moving target, included in the composite signal whose spectrum is rearranged by the rearrangement unit, and extract the moving target component included in the composite signal whose spectrum is rearranged by the rearrangement unit.