In an assembly method of a magnetic fluid seal (100) that includes a magnetic field forming member (130) divided in a circumferential direction, a magnetic pole member (120) including a pair of magnetic fluid retaining portions (121, 122) and a coupling portion (123) that couples them, a first bearing (160) and a second bearing (170), a step of fixing the first bearing (160) to a shaft (400) in a state in which the shaft (400) is directed in a vertical direction, a step of attaching the magnetic pole member (120) from above the first bearing (160), a step of fixing the second bearing (170) to the shaft (400) from above the magnetic pole member (120) to thereby fix the magnetic pole member (120) in a state in which the magnetic pole member (120) is positioned with respect to the shaft (400); and a step of attaching the magnetic field forming member (130) between the pair of magnetic fluid retaining portions (121, 122) are performed in order.

Provided is a bearing with a magnetic fluid seal reliably maintaining sealing of a rolling element section in the bearing and having a structure ensuring high productivity. In a bearing with a magnetic fluid seal according to the present invention, a plurality of rolling elements 7 are disposed between an inner ring and an outer ring, and a ring-shaped magnet is arranged at an opening side of the inner and outer rings so as to retain magnetic fluid, so that the plurality of rolling elements are sealed. The magnet is magnetized so that magnetic poles are oriented in an axial direction. A ring-shaped pole plate is arranged to be in contact with an outer side surface of the magnet in the axial direction. Outer-ring-side magnetic fluid is retained between the outer ring and the magnet, and inner-ring-side magnetic fluid is retained between the inner ring and the pole plate.

Provided is a bearing with a magnetic fluid seal reliably maintaining sealing of a rolling element section in the bearing and having a structure ensuring high productivity. In a bearing with a magnetic fluid seal according to the present invention, a plurality of rolling elements 7 are disposed between an inner ring and an outer ring, and a ring-shaped magnet is arranged at an opening side of the inner and outer rings so as to retain magnetic fluid, so that the plurality of rolling elements are sealed. The magnet is magnetized so that magnetic poles are oriented in an axial direction. A ring-shaped pole plate is arranged to be in contact with an outer side surface of the magnet in the axial direction. Outer-ring-side magnetic fluid is retained between the outer ring and the magnet, and inner-ring-side magnetic fluid is retained between the inner ring and the pole plate.

A pivot assembly bearing includes a shaft, a sleeve provided coaxially with the shaft, and a pair of rolling bearings arranged to be separated from each other in an axial direction between the shaft and the sleeve. The sleeve includes a ventilation path configured to communicate a region surrounded by the shaft, the pair of rolling bearings, and the sleeve with the outside of the sleeve.