Image Number 5 for United States Patent #5944427.
A cross-sectional shape of a shaft body 1 perpendicular to its axis O has a shape defined by a closed curve having a plurality of maximal points M.sub.1, M.sub.2 and M.sub.3 whose distances from the axis are maximized about the axis O and a plurality of minimal points N.sub.1, N.sub.2 and N.sub.3 whose distances from the axis are minimized. This cross-sectional shape has a groove forming region provided with one groove 1b.sub.1 at least between the maximal points M.sub.1 and M.sub.2. When a bearing body 2 rotates on a CCW side with respect to the shaft body 1, the groove 1b.sub.1 is so arranged that an outer peripheral length a.sub.1 in the forward rotational direction exceeds an outer peripheral length b.sub.1 in the reverse rotational direction. Thus, a dynamic pressure gas bearing structure which can prevent galling of the shaft body and the bearing body by shifting the shaft body and the bearing body to a noncontact state at a low rotational frequency is obtained