is shown a hub 9 serving as a rotating member on the outer periphery of which is fixed with a magnetic recording disc and the like is externally fitted in a press fit state to the projecting end 1 a of the shaft 1 projecting from the opening of the sleeve 3 in this embodiment a rotor magnet 10 is attached to the outer periphery of the part closer to the base of the hub 9 further a stator core 12 wounded with a stator coil 11 is attached to the base 5 so as to face the rotor magnet 10 the rotor magnet 10 and the stator core 12 configure a driving unit of the spindle motor for applying a rotation driving force to between the shaft 1 and the sleeve 3 when the hub 9 the shaft 1 and the thrust flange 2 are rotated by the driving unit of the spindle motor the dynamic pressure is generated at the lubricating oil 6 of the respective locations by the radial dynamic pressure generating groove 7 in the radial direction and the thrust dynamic pressure generating groove 8 in the thrust direction the hydrodynamic bearings radial bearing and thrust bearing allow the shaft 1 and the thrust flange 2 to be rotatably supported with respect to the sleeve 3 and the thrust plate 4 in a non contacting manner while maintaining the micro gap the shaft 1 and the thrust flange 2 are formed using sus 303 which is an austenite stainless the shaft has a diameter of.