To provide an optimal C/N ratio design/allocation machine which is capable of establishing a design technique for designing optimal performance allocation that optimizes the effect of plant-equipment investment satisfying an end C/N ratio, and to provide an optimal C/N ratio design/allocation program and an optimal C/N ratio design/allocation method.

The optimal C/N design/allocation machine 1 is a means for carrying out a performance allocation among a key station, a relay station, and an end station so as to satisfy the end C/N ratio of the end station installed at an end from the key station via the relay station in a digital terrestrial broadcasting system SFN network. The machine is equipped with an input means 3, an output unit cost functional setting means 5, an output number-of-household functional setting means 7, a C/N ratio allocation curve calculating means 9, a figure-of-merit curve calculating means 11, an optimal allocation curve calculating means 13, and a performance allocation calculating means 15.