A signal processing system manages terminal numbers as a whole system without being affected by exchange of substrates and performs signal processing of intended object. A control unit sequentially assigns terminal numbers to substrates in numerical order of slots of each kind and validates only terminal numbers regarding the slot where the relevant kind of substrate is inserted. Information indicating regions of different terminal numbers in a space where the number of input/output terminals are more than those of the whole system is retained corresponding to the substrate of each kind. Based on a command specifying input/output signals by the terminal numbers in the space, terminal numbers of a substrate of the kind corresponding to the region including the specified terminal numbers are obtained, and processing corresponding to the command is executed only when those terminal numbers are valid in the substrate of the kind.