Abstract: A shaft integral with a rotary polygon mirror is fitted in a sleeve having dynamic-pressure generating grooves to construct a hydrodynamic bearing. A bearing surface of the sleeve is subjected to an electroconductivizing treatment through formation of a chemical conversion film, and an electrodeposition film having a lubricating filler such as a silicon-based resin, inorganic particles, or the like dispersed therein is formed thereon. The film can be formed by electrodeposition which is simpler than plating, and wear resistance and lubricity of the bearing surface can be improved remarkably. The bearing structure prevents wear from occurring during low-speed rotation.