A support structure including a cylindrical insertion hole. Collars each having a flange formed at one end are press-fitted from both ends of the insertion hole, and fixing means are inserted into the collars. One end of the insertion hole is formed as a small diameter portion, and another end thereof is formed as a large diameter portion. The collars include a small diameter collar of which a press-fit portion has an outer diameter which is press-fitted into an inner diameter of the small diameter portion, and a large diameter collar of which a press-fit portion has an outer diameter which is press-fitted into an inner diameter of the large diameter portion.