Abstract: A reverse rotation prevention device and a magnetic fluid seal mechanism disposed in front of the reverse rotation prevention device are provided. The reverse rotation prevention device comprises an inner ring, an outer ring disposed outside the inner ring, and a plurality of rollers disposed between the inner ring and the outer ring. The magnetic fluid seal mechanism comprises a cylindrical member that is a magnetic body, a ring-shaped magnet, a first magnetic plate and a second magnetic plate, and a magnetic fluid held by a magnetic force. A cylindrical intermediate member that is a non-magnetic body disposed between the inner ring and the cylindrical member is further provided.