In a spindle motor in which its weight is decreased while maintaining the rigidity of a bearing to a large value, the widthwise dimension of a bearing cartridge assembly 11 is set so that the upper outer ring end portion 12b of the outer ring 12 of the bearing cartridge assembly 11 protrudes from a hub main body 6A. Since the lengthwise dimension of a hub 5A is smaller than that of a prior art, the weight and cost can be decreased that much. Further, the lengthwise dimension of the hub 5A is smaller than that of the prior art, a space portion is increased and the space portion can be employed as a space for arranging various kinds of members. Since the upper outer ring end portion 12b protrudes from the hub main body 6A, fitting pressure is not exerted on the upper outer ring end portion 12b of the outer ring 12 upon fitting, so that the generation of unnecessary deformation or the like can be avoided.