A method is presented for calculating the unbalance vibration of a rotating shaft system consisting of variable cross sections, disks, journal bearings and unbalances. Property of oil film bearing is assumed to be that of the springs and dampers including those which give resistance to the change of inclination angles and velocities of inclination angles. These latter springs or dampers will be called "rotational" springs or dampers. These coefficients of cylindrical journal bearings are derived from the short bearing approximation. It is concluded that the property of rotational springs and dampers of oil film in the bearing cannot be neglected, and that the calculated results obtained by means of this method agree very well with most of the experimental results for the case of rotating shaft systems with two or three cylindrical journal bearings, that of an overhung shaft system, and that of a shaft system with distortion.