To provide an inexpensive bearing structure automatically aligning by absorbing inclination or a deviation between bearings, suppressing the leakage of air around a shaft, and having the small number of parts.

A contacting surface of a bearing 4 with a shaft 3 is made to be an arc-shaped surface 4a having a projecting center portion in a bearing cross-section, thereby absorbing a deviation from a center of the bearing 4 or warping of the shaft 3. Therefore, a clearance dimension between the bearing 4 and the shaft 3 can be decreased, so that airtightness of the bearing portion is improved. A bearing member for absorbing inclination and a deviation on a shaft center between the bearings is not required, so that a compact and inexpensive bearing structure can be provided.