A cap fixing structure is provided, which is excellent in operability and can be easily assembled. An outer shaft barrel to be fixed with a clip is formed on the outer peripheral surface with an opening, and inside the outer shaft barrel, there is fixedly disposed a clip spring having an elastically displaceable elastic piece portion. The clip comprises a clip main body disposed outside of an outer shaft barrel, and a base portion to enter into the outer shaft barrel from the opening formed in the outer shaft barrel. The base portion of the clip is stopped from being fell out of the opening by the clip spring with elastically contacting the elastic piece portion of the clip spring inside said fixed member so that the clip is fixed to the fixing member. The clip displaces the elastic piece portion so as to be rockable relative to the outer shaft barrel.