A partition member is provided with an elastic body for absorbing hydraulic pressure fluctuation of the primary liquid chamber and a frame member for supporting an outer circumferential portion of the elastic body while aiming to prevent the rotation of the elastic body. A relief aperture communicating between the primary liquid chamber and the secondary liquid chamber is located on the outer circumferential side in the elastic body supporting region of the frame member. A relief valve for opening and closing the relief aperture is integrally formed on the outer circumferential side of the elastic body. The relief valve is formed of a pair of right and left relief valves. A width across flat sections are formed on a thick-walled outer circumferential section of the elastic body which is located between the right and left relief valves, such as to serve as a detent means.