There is provided a means for preventing wear caused by the contacting/sliding of a thrust hydrodynamic gas bearing surface when a spindle motor is started. A cylinder 4 of a radial hydrodynamic gas bearing that has radial hydrodynamic grooves in an outer circumferential surface thereof and a disk 3 of a thrust hydrodynamic gas bearing that has thrust hydrodynamic grooves in an upper face thereof are disposed on an upper end of an axial center of a stator core 2 having a stator 2a around which a motor coil 7 is wound, a hollow cylinder 6 whose inner surface facing the cylinder 4 of the radial hydrodynamic gas bearing is smooth and a rotor magnet 8 facing the motor coil 7 are disposed on a hub 5 acting as a rotational member, a load in a radial direction is supported by the radial hydrodynamic gas bearing, and a load in a thrust direction is supported by using the thrust hydrodynamic gas bearing together with a magnetic bearing consisting of the stator 2a and the rotor magnet 8.