A vibration isolation device including a stationary housing; a movable top plate positioned horizontally above the stationary housing; an airtight flexible member forming an airtight pressure chamber between the movable top plate and the stationary housing; a vibration-free movable base having a mounting plate portion; and a dome-shaped contacting portion, provided between opposed surfaces of the movable top plate and the mounting plate portion. The movable top plate is moved up and down by varying an internal pressure of the airtight pressure chamber. The vibration-free movable base is moved up and down via the dome-shaped contacting portion. The vibration isolation device includes a biasing device, positioned inside the airtight pressure chamber for holding the planar centers of the movable top plate and the mounting plate portion in contact with each other when the internal pressure of the airtight pressure chamber is smaller than a predetermined value.