To ensure fastening strength at the time of fixing an additional member, and improve the performance of a bearing and reliability by inserting and fixing another cylindrical member at the cylindrical part outer periphery of a rotor hub, fixing a fixing member for fastening the additional member for a motor at the rotor hub, and forming a radial bearing part in a gap between the cylindrical member and a bearing member.

A cylindrical member 121 is inserted and fixed at the outer periphery of the cylindrical part 101C of a rotor hub 101, serving as a rotating shaft at the time of the rotation of a motor, is constituted of an SUS material or the like. A radial dynamic pressure fluid bearing which is filled with a lubricant 104 and capable of relative rotation is formed in a gap between a bearing member 103 and the cylindrical member 121. Moreover, for the lubricant 104, it is preferably to use the one with low-evaporation for reliability. A thrust member 105, serving as a thrust bearing, is constituted of a member having a material high in hardiness, and for example, ceramic or SK material with quenching treatment applied, or the like is preferable from the stand point of reliability.