Aircraft designers determine the optimum aircraft configuration to meet performance requirements. Aircraft secondary power systems are very important for aircraft operation, however, traditionally these systems have not been considered in detail while the aircraft configuration and specifications are preliminary studied. Therefore, we constructed an aircraft conceptual design tool considering the many aircraft systems. Furthermore, we applied this design tool to a simple design problem taking into account two different kinds of secondary power system architectures (i.e. the conventional bleed air system and the more electric system), and discussed how the introduction of new aircraft systems affects results. Although the present method is theoretical and conceptual with limited applicability, the effect of the aircraft's secondary power system upon the concerning aircraft specifications was made clear both for the bleed air system and the more electric system.