To block the transmission to a vehicle body side of the vibration due to the cavitation phenomenon occurred in a primary liquid chamber so as to prevent the generation of noises, at the same time, to make the device compact, and to improve the fitting accuracy to obtain the reliable positioning, a first metallic fitting and a second metallic fitting are connected by an insulator. A primary liquid chamber and a secondary liquid chamber formed inwardly are partitioned by a partition member and communicated therebetween by an orifice passage. The partition member is floatingly supported between an extended portion of the insulator and an outer peripheral thick wall portion of a diaphragm, and the tuning is performed to generate the rigid resonance at the predetermined frequency. An outer ring is provided in the outer peripheral thick wall portion so as to be securely fixed by a fixing portion formed by bending an end of an outer cylindrical fitting. The floatingly supporting structure does not become large-sized and complicated since the partition member is simply floatingly supported.