PURPOSE: To obtain a long life at a low cost, by turnably fitting with a clearance the second ferromagnetic material of circular annular shape in the first ferromagnetic material, which forms a circular annular shape having a section in the diametric direction in a recessed shape, through magnetic fluid, based from a lubricant, and magnetizing either the first or second ferromagnetic material.
CONSTITUTION: A cylindrical bottomed rotary unit 2, which vertically provide a rotary shaft in the center, is provided being opposed to the first ferromagnetic material 1 which forms a circular annular shape having a section in the diamet ric direction in a recessed shape. The second ferromagnetic material 5, which is provided over the whole periphery of an edge part 4 of said rotary unit 2, is magnetized in the diametric direction. Next, magnetic fluid 6, based on a lubricant, is provided between the first ferromagnetic material 1 and the second ferromagnetic material 5. Further the magnetic fluid 6 is formed by suspending magnetite of fine oxidized iron dust in an organic solvent of ethers. Accordingly, the cost can be reduced by ensuring a long life even if a radial load is applied.