For optimal design of a system consisting of multiple subsystems, which requires optimization and integration of the subsystems, consideration of the effects of interfaces between the subsystems raises evaluation problems,because even when optimal designs appear obtainable for the individual subsystems,the design of the actual entire system including those subsystems may not necessarily be optimal. This study addressed the optimization of a medium frequency (AM) amplifier, by assuming that the AM amplifier includes two subsystems:an antenna amplifier, and a receiver that acts as the load of the antenna amplifier. An analysis taking the effects of the interface between the subsystems into consideration was carried out to obtain an optimal design of the entire system. This showed that the entire system could be tuned efficiently to the desired characteristics by a two-phase design procedure, together with optimization of the subsystems.