To provide a vibration isolating device that can reduce the dynamic spring constant in the fore-and-aft direction of a vehicle and can reduce effectively the indoor noise upon acceleration and running at high speed. The device has a cylindrical main body fitting to be fixed to a vehicle body side, a boss fitting to be coupled to a vibration generator side, a rubber elastomer as a vibration isolator interposed between both, front and rear stopper rubber portions attached to a coupling member secured to an upside of the boss fitting, and a stopper member disposed in front of and in the rear of the stopper rubber portions and to be fixed to a vehicle body side, wherein a small cavity is provided in at least one of the front and rear stopper rubber portions.