To create a finite element model of twisted cord where all of tension rigidity, flexural rigidity, and radial direction compression rigidity match a target value.

In a computer, on the basis of a finite element model dividing twisted cord 3 into two concentric layers, initial values of a physical property value and a diameter of external material 1, and a physical property value and a diameter of internal material 2 are set, and target values of tension rigidity, flexural rigidity, and radial direction compression rigidity are set (S1 and S2). The physical property value of the external material 1, the physical property value of the internal material 2, and a value of the diameter of the internal material 2 in the twisted cord 3 are varied, and on the basis of a predetermined theoretical formula and approximation formula, the tension rigidity, the flexural rigidity, and the radial direction compression rigidity are calculated. If it is determined that calculated values of the tension rigidity, the flexural rigidity, and the radial direction compression rigidity are matched with the target values within a predetermined error, the physical property value of the external material 1, the physical property value of the internal material 2, and the value of the diameter of the internal material 2 which are used for calculation are output (S3 to S6).