It is an object to improve bearing rigidity in a thrust direction at high temperatures and reduce a torque at low temperatures. An axial member is arranged in such a manner that an outer circumferential surface of an axial part is opposed to an inner circumferential surface of a bearing sleeve with a radial bearing gap interposed therebetween, and both end faces of a flange part are opposed to one end face of the bearing sleeve and a bottom face of a housing with thrust bearing gaps interposed therebetween, respectively. In this manner, the axial member is supported by dynamic pressures generated in the respective bearing gaps in the thrust direction in a non-contact manner. The flange part of the axial member is formed of a resin in such a manner that its linear expansion coefficient in its axial direction is equal to or larger than that of the housing.