This report shows some measurement results of the flexural vibration of actual railway vehicles and presents a new analytical method to investigate the vibration. Stationary vibration tests show that recent lightweight railway vehicles often have complicated three-dimensional (3D) vibration mode shapes. A new analytical method is proposed to simulate and study measures to reduce such complicated vibration. In this method, the carbody is modeled as a box type structure consisting of plates and beams. The condition to connect components is satisfied by introducing artificial springs at their joints. The formulation procedure of the method to analyze natural modes and frequency response to vertical track irregularities are described in brief. The numerical results are compared with the measured data for an actual railway vehicle to examine the validity of the method.