A sealing device employing a magnetic fluid for sealing off a vacuum side and an atmosphere side includes two rolling bearings disposed on both sides of the magnetic fluid seal. The magnetic fluid fills the lubrication part of the rolling bearing disposed toward the vacuum side and a magnet is attached to the outer ring toward the vacuum side of said rolling bearing. A ring-shaped yoke formed from a magnetic material and freely fitting into a rotation shaft is attached to the side of the magnet opposite the outer ring of the rolling bearing.