A calculation method, by which suitable estimation of vibration and strength concerning crank shaftings of recent 2 stroke cycle marine diesel engines can be got, is desired, because other method proposed before cannot evaluate stiffness of the crank throws completely in case of such type engines, thus calculation results on the vibration are unsatisfactory. The authors have been trying to make an analysis scheme for them, and introduce in this report a new method for the calculation of natural frequencies of the shaftings. The model employed has degrees of freedom for axial and torsional directions, and their coupling action is also included. In the new method, FEM analysis is used for the computation of crank shaft's stiffness, and interaction between the consecutive crank throws is described correctly. Calculated values of the natural frequencies correspond well to measured ones.