This invention prevents seizure of a dynamic pressure gas bearing caused upon swinging contact between a motor shaft and a sleeve and an increase in contact friction torque. It also detects rotation of auxiliary bearings. A motor includes auxiliary bearings in series with a dynamic pressure gas bearing, and a non-contact detent torque generation mechanism parallel to the auxiliary bearings suppresses rotation of the auxiliary bearings. Where Ta denotes rotation-time viscous friction torque of the dynamic pressure gas bearing, Tka denotes contact friction torque possibly causing damage to the dynamic pressure gas bearing, Tb denotes rotation friction torque of the auxiliary bearings, and Tdmax denotes maximum torque generated when rotation of the auxiliary bearings is suppressed by the non-contact detent torque generation mechanism, (Ta+Tka)>(Tb+Tdmax)>(Ta), and the rotation detecting means detects the rotation of the auxiliary bearings.