There is provided a signal processing device including a signal generation unit that generates a control signal for controlling an imaging device connected via one cable, a signal superimposition unit that superimposes the control signal generated by the signal generation unit on a video signal received from the imaging device via the cable without an influence on display of a video corresponding to the video signal, and a transmission unit that transmits the signals superimposed by the signal superimposition unit to the imaging device via the cable.