Suppression of vertical bending vibration is essential to improve ride comfort on railway vehicles. For this purpose, a primary suspension damping force control system is being developed. This paper describes the composition of the system and reports on the results from vehicle running tests on some Shinkansen lines using actual Shinkansen vehicles fitted with the developed variable primary vertical dampers. The results of these tests demonstrate that this system is effective in reducing vertical vibration acceleration in the first bending mode of the car body and improves ride comfort. In addition, a progress report is also given on its ongoing development.