Through quantitative analysis of the mechanism of a hydraulic engine mount with a simple structure, it has been found that the mount functions as a "Velocity Amplifying Dynamic Damper". It was also found that effective utilization of this function provided the following advantages : the dynamic damper can be tuned to an extremely low frequency resonance range and given a compact structure, while the requirement for vibration damping effect can be satisfied at the same time. Then, this function was proven practical through applying it to analysis for reducing vehicle vibrations.