The thrust member is inserted into the inner circumferential surface of the housing, to make the end face of the thrust member contact with the lower side end face of the flange portion, and at the same time, to make the upper side end face of the flange portion contact with the lower side end face of the bearing sleeve. This stated is that the thrust bearing gap is zero. Then, the thrust member is made to relatively move with respect to the housing and the bearing sleeve in the axial direction together with the axis member, with a dimension δ(δ=δ1+δ2) that is equivalent to the sum of the thrust bearing gap (size is δ1) of the first thrust bearing portion and the thrust bearing gap (size is δ2) of the second thrust bearing portion. Then, as the thrust member is fixed to the housing at that position, the predetermined thrust bearing gap δ(δ=δ1+δ2) is formed.