In order to develop sufficient vibration damping performance and effectively prevent transmission of goading vibrations and others in a vibration damping device using an electrorheological fluid, if the moving directions of vibration input side member and vibration output side member of the device are opposite to each other, a voltage applied to electrodes in the device is increased to increase the viscosity of the electrorheological fluid, while if absolute value of vibration acceleration velocity in the vibration input side member exceeds a given value, a voltage applied to the electrodes is always decreased to decrease the viscosity of the fluid.