To prevent a shaft and a sleeve from sliding and rotating while contacting with each other until dynamic pressure is generated or after dissipation of the dynamic pressure.

A rotor boss 4 integral with the shaft 1 supports a rotary polygon mirror 11 on its upper surface and supports a rotor 12 on a lower surface. In motor stopping or starting, for a while until sufficient dynamic pressure is generated in oil in a bearing clearance by dynamic pressure generating grooves 3a, 3b, the shaft 1 tilts into contract with the sleeve 2. The shaft tilting is prevented by disposing first and second magnets 15a, 15b in an opposed manner on an outer peripheral surface of the sleeve 2 and on an inner peripheral surface of the rotor boss 4 and by bringing the magnetic force centers of them in line with each other.