This study deals with a patient-specific modeling method that generates a finite element model based on the X-ray CT images. The basic idea of our modeling method is to express an objective shape with small tetrahedral elements. This paper proposes a new meshing algorithm that controls element size according to shape or density information extracted from the CT images. For the automated modeling, we introduce “form factor” that indicates degree of complexity of the objective shape. The factor at a remarking point is easily obtained by a simple calculation using a local inspection region around the point. The new method produces a finite element model with variable mesh size. To validate the method, we discuss following three issues : proper volume of the inspection region for precise modeling, accuracy verification of stress analysis, and required working time for modeling and analysis. The computational results by the proposed method shows good analytical precision with a smaller FE model.