Abstract: A holding structure includes a bearing holder including a cylindrical holder portion into which a ball bearing is internally fitted from one side in an axial direction of a shaft, and a positioning portion on another side in the axial direction of the holder portion and abutting on the ball bearing; and a mounting plate having a cylindrical mounting portion in which a portion of the holder portion is press-fitted. An inner surface of the holder portion includes an adhesion surface bonded to an outer peripheral surface of the ball bearing, a relief surface having an inner diameter larger than an inner diameter of the adhesion surface, and a step surface connecting the adhesion surface and the relief surface. An axial position of the step surface overlaps the ball bearing engaged to the bearing holder.