This paper presents a structur evaluation method with the use of area of stabilizable space under the condition in which system has a input saturation. In this paper, a mathematical model and a normalized model of the Furuta pendulum were developed. Stabilizable space of each model was derived. Changes of area of each stabilizable space for changes of physical parameter were calcurated. The relation of each model was discussed because an actual model and a normalized model have different state space. As a result, the presence of a physical parameter which maximizes area of stabilizable space was indicated. In conclusion, the effectiveness of the proposed method was verified by a numerical simulation with the physical parameter.