In the present report, the authors propose a practical and useful method for identifying the characteristic matrices (general name of the mass, damping and stiffness matrices) of mechanical structures. The characteristic matrices of mechanical structures can be identified in a much shorter CPU time by the proposed method than by previous methods also proposed by the authors. In this paper, the theory of the proposed method is explained. Three examples are demonstrated in order to prove that the method is valid. practical and useful. The first example shows that the method can identify physically valid characteristic matrices. The second shows that modal parameters from identified characteristic matrices correspond well to the result from the Poly-Reference method. In the third example, a cylinder-head of an actual engine is identified by the proposed method.