A signal processing device includes: signal processing circuits. The signal processing circuit includes an input/output circuit configured by an input circuit serving as an input interface of a signal of a predetermined frequency band and/or an output circuit serving as an output interface of a signal of the frequency band and performs transmission of a signal of the frequency band between the signal processing circuit and another signal processing circuit. The output circuits of one and another signal processing circuits include circuits having the same configuration. The input circuits of the one and another signal processing circuits include other circuits having the same configurations. The input/output circuits of the one and another signal processing circuits can perform transmission of a signal of the predetermined frequency band even when any one of transmission media having mutually different characteristics is mediated.