A signal processing device is provided, which includes a pulse compressing module configured to generate a pulse compressed signal obtained by performing pulse compression on a reception signal that is a reflection of a transmission signal transmitted to outside the device, a pseudo signal generating module configured to generate, based on the reception signal, a pseudo signal of which a pseudo main lobe portion corresponding to a main lobe of the pulse compressed signal has a lower signal level than signal levels of pseudo side lobe portions corresponding to side lobes of the pulse compressed signal, and a side lobe removing module configured to remove the pseudo signal from the pulse compressed signal.