A cylindrical sleeve is rotatably fitted over a fixed shaft erected on a base, the sleeve including an outer collar part at an outer periphery of the lower end portion thereof, a slip-out preventing member for preventing the slip-out from the fixed shaft while allowing the sleeve to rotate is provided on the base, the slip-out preventing member including an inner collar part that engages with the outer collar part in the slip-out direction. A hub is provided on the upper end portion of the sleeve, a pair of upper and lower radial bearings formed with a dynamic pressure generating groove are provided on the inner peripheral surface of the sleeve, and a thrust bearing formed with a dynamic pressure generating groove is provided at the lower end face of the sleeve.