While applying an ultrasonic vibration to a housing 7 and/or a bearing sleeve 8, the outer peripheral surface 8d of the bearing sleeve 8 is press-fitted into the inner peripheral surface 7c of the housing 7 with a predetermined interference, and is welded thereto. During the press-fitting, the region of the inner peripheral surface 7c of the housing 7 coming into contact with the bearing sleeve 8 is melted or softened by the action of the ultrasonic vibration, so that, as compared with a case in which only press-fitting is conducted, the requisite press-fitting force at the time of press-fitting can be substantially reduced.