There is provided a signal processing device that includes a processing unit configured to collect, through a microphone, a mixed sound signal as a mixed sound of a speaker reproduction signal and a target signal, input a first suppression signal resulting from suppression of the speaker reproduction signal from the mixed sound signal by linear processing, the speaker reproduction signal, and the mixed sound signal collected through the microphone, and output a second suppression signal resulting from further suppression of the speaker reproduction signal from the first suppression signal by non-linear processing.