PURPOSE: To provide an excellent vibration isolating effect against input vibration in a frequency range responding to a mass of a mass member, by a method wherein a part of the partition part of an actuating member is formed by a mass member, and is resiliently held to an actuating member body through a resilient member.

CONSTITUTION: A part of the partition part of an actuating member body 50 is formed by a mass member 52, and the mass member 52 is resiliently held to the actuating member body 50 through a rubber resilient member 54. Thereby, deformation of the resilient member 54 forces the mass member 52 to be moved in a reverse phase to that of the actuating member body 50, causes excellent suppression of an increase in a fluid pressure in a chamber part between the actuating member body 50 and a partition member 34, and in turn, enables excellent suppression of an increase in vibration transmissivity. In which case, resonance of the mass member 52 enables provision of a vibration isolating effect excellent to input vibration in a frequency range responding to the mass of the mass member 52.