Disclosed is a shaft member for a hydrodynamic bearing device which allows production of a shaft member of smaller size at low cost and which suppresses ion elution from the resin portion, thereby maintaining cleanliness in the hydrodynamic bearing device and making it possible to exert a desired bearing performance. A shaft member 2 is equipped with a shaft portion 2a and a flange portion 2b protruding radially outwards from the shaft portion 2a, and has a composite structure composed of a metal material and a resin composition, in which a resin portion 21 is formed by injection molding of a resin composition containing as a base resin a polyphenylene sulfide (PPS) whose Na content is not more than 2,000 ppm and containing PAN type carbon fibers as a filler.