An aspect of the present invention is directed to a method for forming a mirror-reflecting film on a waveguide in an optical wiring board, characterized in that a multilayer film, in which a base, a metal layer and an adhesive layer are layered in this order, is used, and the metal layer is transferred and bonded to an inclined face for mirror-reflecting film formation provided on the waveguide, with the adhesive layer of the multilayer film intervening. The present invention provides a method which, when forming a mirror-reflecting film on a waveguide in an optical wiring board, enables inexpensive and easy formation of the mirror-reflecting film, using the smallest quantity of metal possible and employing comparatively simple facilities and techniques.