A vibration isolator having a pair of pressure receiving fluid chambers between an outer cylinder and a mounting member, at two end sides along a main amplitude direction. A rubber elastic body changes the internal volumes of the pair of pressure receiving fluid chambers in directions opposite to each other, and fluid flows from the pressure receiving fluid chambers to an auxiliary fluid chamber through one of two orifices and flows from the auxiliary fluid chamber to the pressure receiving fluid chambers through the other orifice. Since a fluid pressure in the auxiliary fluid chamber is kept approximately constant, the fluid in the pair of pressure receiving fluid chambers smoothly flows, with a low resistance, into the auxiliary fluid chamber through the orifices. Therefore, any rise of the fluid pressure in the pressure receiving fluid chambers may be suppressed, such that rise of the dynamic spring constant may be suppressed.