In a disk drive device, a magnetic recording disk is to be mounted on a hub. A base plate rotatably supports the hub through a bearing unit. A projecting portion is formed on the upper surface of the base plate having a cylindrical side surface centered along the rotational axis of the motor. A laminated core is formed by laminating magnetic steel sheets and has a ring portion and a plurality of teeth radially extending from the ring portion. The disk drive device has a tubular vibration-deadening ring. The outer surface of the vibration-deadening ring is press-fitted into the ring portion at least at a position, along the motor's rotational axis, closer to the upper surface than to the lower surface of the laminated core; and the inner surface of the vibration-deadening ring is fixed to the side surface of the projecting portion.