Method for producing fluid dynamic pressure bearing

A method includes compacting metal powder including at least not less than 70% by weight of particles with diameters of not more than 45 μm to obtain a bearing material, sintering the bearing material, forming grooves for generating dynamic pressure on the sintered bearing material, and performing steam treatment to the sintered bearing material with the grooves to form a ferrosoferric oxide (Fe3O4) membrane on a porous surface of an inner surface or on porous surfaces of an inner surface and both end surfaces. Thus, gaps between particles become small because diameters of the particles of material powder of a powder sintered bearing material are approximately even and fine and are even small pores. As a result, sealing pores on the surface due to steam treatment is easy, and dynamic pressure cannot be leaked.