An axial end of an outer peripheral surface of the inner ring of the bearing unit for an air turbine has an inclined surface (23) having a diameter that changes from large to small toward the downstream side with respect to the supply direction of axial compressed air. The seal member (30) is configured only by an elastic material without a metal core, and has a base part extending in a radial direction and a elastically deformable lip part extending from a radially inner end of the base part and inclined to the downstream side with respect to the supply direction of the compressed air. When the compressed air is not applied, an inclined surface, which is positioned at an upstream side with respect to the supply direction of the compressed air, of the lip part is in contact with the inclined surface of the inner ring. When the compressed air is applied, a contact area between the inclined surface, which is positioned at the upstream side with respect to the supply direction of the compressed air, of the lip part and the inclined surface of the inner ring becomes smaller, as compared to when the compressed air is not applied.
