PURPOSE: To provide an end surface with excellent transparency by a simple treatment by pressing a transparent plate cover body onto the end surface to be treated under the interposition of a transparent liquefied body by a pressing means.

CONSTITUTION: The end part of an optical fiber bundle 1 in which a number of optical fibers are bundled is held by an end holder 2, and a cylindrical pressing body 3 is screwed to the end part holder 2, whereby a cover body 4 is pressed onto the end surface 1f to be treated of the optical fiber bundle. The cover body 4 is formed of a transparent acrylic resin plate according to the form of the end surface if to be treated of the optical fiber bundle 1, and the thickness is about 0.5mm. A liquefied body 7 using a transparent liquefied silicone resin is interposed between the cover body 4 and the end surface 1f to be treated. For example, the cover body 4 onto which the liquefied body 7 is dropped is pressed onto the end surface 1f to be treated, whereby a thin film of the liquefied body 7 is formed between the cover body 4 and the end surface 1f to be treated.