A signal processing device includes a switching receptor, a storage, and a signal processor. The switching receptor receives switching of a speaker serving as a supply destination of a signal. The storage stores an optimal setting, which is obtained by measuring characteristics of the speaker selected by the switching, in association with the switching of the speaker. The signal processor reads out the optimal setting, which is associated with the switching received by the switching receptor, from the storage, and uses the optimal setting to process the signal to be supplied to the speaker.